Presidents, Congress, and the Use of Force

William Howell Harvard University Littauer Center #228 Cambridge, MA 02138 [email protected]

Jon Pevehouse University of Wisconsin 110 North Hall; 1050 Bascom Mall Madison, WI 53706 [email protected]

We thank the Center for American Political Studies at Harvard University and the Wisconsin Alumni Research Foundation for financial support; and Kevin Warnke and Doug Kriner for research assistance.

Debates over Congress’s involvement in foreign military engagements trace back at least to the Republic’s founding. But irrespective of the normative issues at stake (e.g., should Congress shape foreign policy?), a basic point of fact remains unresolved: can Congress effectively constrain presidents from unilaterally exercising force abroad? While illustrative case studies abound, few empirical investigations systematically address the topic. In principle, Congress should contribute to the politics surrounding the use of military force. The Constitution vests Congress with the power to raise and support armies, to provide and maintain a navy, and to regulate the military forces, all of which make “Congress a major participant in foreign policy” (Fisher 1998: 178). Beyond their enumerated powers, Congress can cut off a mission’s funding; its members can appeal to public opinion; as they can kill other aspects of the president’s legislative agenda (Lindsay and Ripley 1993: 22-35). While the president retains considerable discretion to use force when (and as) he pleases, Congress can increase the marginal costs of foreign military ventures. In many instances – e.g. when presidents face particularly controversial or risky foreign conflicts – congressional support or opposition may prove decisive. The existing empirical literature on the use of force, however, does not examine whether presidents balance their “preference for action” (Ostrom and Job 1986: 544) against Congress’s stated interests. While it demonstrates that elections, public opinion, and the economy influence decisions to deploy U.S. military forces abroad, this literature regularly ignores the influence of domestic political institutions. Rarely are any measures of congressional relations with the president included in statistical models on the use of force; and when included, they are crudely specified, typically nothing more than an indicator variable for divided government (Gowa 1998; Fordham 2002).

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We revisit the event-count models used to predict uses of force, adding appropriate measures of congressional support for the president. Our findings are unambiguous, and run directly against the notion that politics stop “at the water’s edge.” Between 1945 and 1995, partisan support within Congress serves as a significant predictor of the number of foreign military engagements each quarter. Effects are especially large with regards to major military initiatives and persist even when controlling for a host of other domestic and international factors. As partisan support within Congress increases, presidents engage in military initiatives more and more often; but as support within Congress wanes, so does the frequency with which presidents exercise their authority to use military force abroad. This paper proceeds a s follows. The first section reviews the empirical literature on the use of force in the international relations subfield, and the theoretical literature on presidential-congressional relations within the American politics subfield. The second section applies these theoretical insights about executive-legislative relations to presidents’ decisions about whether to deploy military troops abroad. The third examines the empirical relationship between the partisan composition of Congress and the number of uses of force during the post-War era. The final section concludes.

Section I: The Relevant Literatures There are, at present, two relevant literatures on the domestic politics of international engagement. One is located within International Relations, the other within American Politics. We consider each in turn.

The International Relations Literature The use of U.S. armed forces as a political bargaining tool (such as the Berlin Airlift, the Cuban Missile Crisis, and ongoing interventions into the Middle East and Central 2

America) represents one of the most potent expressions of executive authority. Not coincidentally, the practice has garnered a large academic following, beginning with the pioneering work of Barry Blechman and Stephen Kaplan in 1978. Blechman and Kaplan were principally concerned with the international conditions (e.g., whether the Soviet Union or China was a party to a crisis, whether troops were already deployed in the region, the relative nuclear capabilities of the United States and the Soviet Union) that lead presidents to initiate lower-level military ventures, what they termed “force without war.” Blechman and Kaplan identified 226 such incidents between 1946 and 1976 and tracked when, and whether, U.S. presidents achieved their strategic objectives. Beginning in the mid 1980s, scholars built upon Blechman and Kaplan’s database to test a confluence of international relations theories about inter-state conflict and political psychology insights into executive decision-making. Cha rles Ostrom and Brian Job’s study (1986) added an important set of domestic variables to the study of the use of force. According to Ostrom and Job, U.S. presidents must create simple decision rules to balance the competing demands of the presidency. As commander-in-chief, chief executive, and “political leader,” presidents “monitor salient dimensions in the domestic, international, and political arenas” before committing U.S. forces abroad. Domestic politics, however, retain special significance. Indeed, in Ostrom and Job’s empirical analysis, the substantive impacts of domestic variables (public aversion to war, a weighted economic misery index, presidential approval, “overall presidential success,” and national elections) on the use of force were consistently as strong if not stronger than their international counterparts (1986: 555). The bulk of studies following Ostrom and Job have examined how the economy and public opinion influence presidents’ decisions to deploy troops abroad. Patrick James and John Oneal (1991) introduced a new variable that tapped international threats to U.S. 3

interests, yet still found that the same domestic political factors that Ostrom and Job introduced were largely responsible for the use of force. Benjamin Fordham (1998) subsequently argued that economic factors and public opinion do not directly shape presidential decision-making, but instead influence how the president views his external environment. The president, according to Fordham, only “sees” opportunities to use force when the domestic economy is poor – when inflation is low and employment high, presidents have few incentives to imperil their reelection prospects with risky foreign military ventures. Other scholars have lodged numerous methodological critiques of the use of force literature. Meernik (1994) has argued that quantitative studies of the U.S. use of force suffer from selection bias: there are myriad domestic and international contexts in which the U.S. does not respond. By only examining actual uses of force, Meernik correctly pointed out, scholars have assembled an incomplete view of the dynamics of presidential decisionmaking. More recently, Mitchell and Moore (2002) and Fordham (2002) have raised important issues of data comparability (scholars use different years in analyzing their hypotheses) and temporal dynamics (uses of force tend to be clustered together in time) which may compromise previous statistical findings. While much divides the protagonists in the use of force literature, one assumption is consensual: Congress is weak.1 Indeed, an assumption of legislative impotence has achieved the status of conventional wisdom: The literature on U.S. foreign policymaking unambiguously demonstrates that because of his constitutional prerogatives and political incentives as well as congressional weaknesses in foreign policy, it is the president who exercises supreme control over the nation’s military actions. (Meernik 1994: 122-3)

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For an exception, see Richards and Morgan (1993).

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Because the president is commander in chief of the military, Congress cannot (or will not) try to constrain his freedom to pick battles, define the scope and duration of conflict, or set the terms by which a conflict ultimately is resolved. While Congress may direct domestic policymaking, its hold over foreign policy is quite tenuous; and when the president decides to exercise military force abroad, members of Congress can only complain on Sunday morning talk shows. For the most part, the president’s authority over military matters is beyond repute. Consider, by way of examples, the work on two of the causal mechanisms which underlie the use of force literature: the diversionary war hypothesis and “rally around the flag” effects. The diversionary war hypothesis suggests that heads of state deploy troops abroad in an effort to distract attention away from poor economic indicators. Advocates of the theory assume that Congress, the bureaucracy, and the public are blind to a leader’s true intentions and, as a consequence, regularly accept on faith proffered justifications for conflicts (for critiques, see Meernik and Waterman 1996; Blainey 1988; Levy 1989). By sending troops abroad, it is supposed, presidents can shift public attention away from a failing economy and rally widespread support, as members of Congress (very much including the opposition party) naturally and automatically fall behind their Chief Executive. Congress, again, is largely absent from most empirical tests for “rally around the flag” effects (Mueller 1973; MacKuen 1983; Ostrom and Simon 1985; Wittkopf and Dehaven 1987; Lian and Oneal 1993). Congress’s stance on military ventures conducted abroad, it is assumed, does not mediate the size or direction of changes in the president’s public approval ratings. While “aggressive foreign behavior [may be] a useful tool for dealing with domestic political problems,” domestic political institutions do not hinder the president’s ability to engage in aggressive foreign behavior (Morgan and Bickers 1992: 26). Quite the contrary, members of Congress are just as susceptible to the rally phenomenon as 5

is the general public (Stoll 1987). As Barbara Hinckley argues, “The use of force shows the clearest conventional pattern: presidents are active and Congress accedes to what the presidents request. On these occasions both Congress and the public rally around the President and the flag” (1994: 80). We question the “unambiguous demonstration” that domestic political institutions do not, or cannot, impede the presidential use of force. Under many circumstances, Congress constrains the president, limiting the size, frequency, and duration of military initiatives conducted abroad. This does not make the president an empty vessel responding to the whims of Congress. The president clearly retains profound informational and tactical advantages over Congress that make him the most powerful actor in U.S. foreign policy (Moe and Howell 1999). Still, the president cannot easily and automatically dupe his political opponents – especially when doing so entails putting American troops in harm’s way. To strip away the institutional setting in which the president operates is to dismiss the institutional politics associated with the use of military force.

The American Politics Literature While the existing use of force literatures gesture toward congressional-presidential politics (DeRouen 1995), the treatment consistently is fleeting. This is unfortunate given the tremendous volume of research on executive-legislative relations within the American politics subfield (see, e.g., Binder 1999; Jones 1994; Mayhew 1991; Peterson 1990; Bond and Fleisher 2000; Krehbiel 1999). Scholars of American politics have developed ample theories with strong micro foundations on interactions between the executive and legislative branches. None of these theories is addressed in the extant use of force literature. Within the American presidency sub-field, a burgeoning body of work examines when presidents will unilaterally set public policy given that Congress and the courts may 6

subsequently undo his actions (Cooper 2002; Howell 2003; Mayer 2001). Using executive orders, proclamations, memoranda, and administrative orders, presidents have managed to impose a wide array of public policies that never would have survived the legislative process. This work demonstrates that the president’s powers of unilateral action – which very much encompass the option to deploy troops abroad – are critically defined by the capacity and willingness of Congress to subsequently overturn him. When large and unified majorities govern Congress, presidents rarely exercise their unilateral powers. As shown elsewhere (Howell 2003), when strong majorities stand in support, the president would do better to engage the legislative process and set policy with firm legislative footings; and when such majorities stand in opposition, the president cannot hope to unilaterally set any public policy of consequence without provoking a congressional response. But when small and divided majorities govern Congress, presidents have incentives to strike out on their own. In this sense, congressional strength marks presidential weakness, and congressional weakness presidential strength. The outcome is hardly accidental, for it is the checks that each institution places on the other that determines the overall division of power. With regards to the use of force, inter-institutional dynamics shift somewhat, as a clear asymmetry defines the relationship between Congress and the president. While members of Congress can punish the president for deploying troops abroad, they cannot readily impel military action in the face of presidential resistance. As such, in this realm – unlike policymaking generally, where Congress has the option of legislating when the president refuses to issue a unilateral directive – Congress’s impact manifests itself principally as a constraint on presidential power. Congressional opposition to the president, as such, should depress the relative number of military initiatives conducted abroad.

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Strangely, no one in American politics has systematically examined whether Congress influences the frequency with which presidents exercise force abroad. Instead, American politics scholars have offered up little more than case studies, some of which herald Congress’s impotence in foreign affairs (e.g. Hinckley 1994; Weissman 1995), others which note celebrated examples of Congress successfully blocking military campaigns (Lindsay and Ripley 1993). But while ready-made theories on the institutional foundations of unilateral powers are easily applied to president’s decision to use military force, the American politics literature is devoid of empirical tests. Rarely are the limits of one field’s treatment of a topic so perfectly complemented by the strengths of another’s. While scholars of American politics have developed rich institutional theories that delineate the conditions under which presidents exercise their unilateral powers, uniformly they have overlooked the conditions under which presidents deploy troops abroad. Meanwhile, international relations scholars have constructed impressive datasets on the use of force, but the theories they test consistently overlook interactions between Congress and the president. Indeed, the international relations treatment of the use of force assumes away legislative constraints on presidential power – just as American politics scholars remain captivated by them.

Section II: Theoretical Micro-foundations As in unilateral policymaking, the relevance of Congress should vary according to its partisan composition. Without enough seats in Congress, and enough discipline within its ranks, the opposition party can do little to derail presidents’ decisions to use force abroad – for as the international relations literature rightly insists, decisions regarding when and where the military intervenes ultimately reside with the commander in chief. But when the opposition party is unified and large, it can credibly threaten to punish presidents who 8

pursue misguided military ventures. Such punishments need not derail or even stall every military initiative. On average, though, viable congressional opposition should decrease the likelihood that presidents will exercise force abroad. But why should the partisan composition of Congress affect the president’s discretion to use force abroad? More specifically, why should members of the president’s party be especially likely to back the president? And why should members of the opposition party, all else equal, be predisposed to object? We offer three answers drawn from the literature on presidential-congressional politics. Shared Electoral Fortunes: Precisely because their electoral fortunes are linked to the president, congressional members of the president’s party have a vested interest in the president’s success – just as members of the opposition party do in his failure. If presidential approval ratings increase when presidents exercise force abroad, as the rally around the flag literature suggests (Mueller 1973; MacKuen 1983; Ostrom and Simon 1985; Wittkopf and Dehaven 1987; Lian and Oneal 1993); and if high presidential approval ratings boost members’ electoral prospects, as the literature on coattails suggests (Campbell and Sumners 1990; Campbell 1986; Ferejohn and Calvert 1984); then, all else equal, members’ willingness to grant the president broad discretion to exercise force abroad should critically depend upon his partisan identification. Presidential uses of force redound to the electoral benefit of members of the president’s own party and, by implication, to the detriment of the opposition party. As such, members of the president’s party, all else equal, ought to actively support the president’s plans to exercise force abroad, as members of the opposition party cautiously may oppose them. Credibility of Signals: With regards to the use of force, as opposed to most domestic policy matters, profound informational asymmetries define relations between presidents and Congress (Schlesinger 1989). Presidents have at their disposal considerable 9

amounts of private information about developments abroad and their impacts on the nation’s strategic interests. Further, Congress has few formal mechanisms for corroborating this information. When a president makes a case for deploying troops abroad, Congress, ultimately, must decide whether or not to take him at his word. Whether, in fact, members of Congress accept a president’s justification for intervening in foreign crises critically depends upon the distance between their respective ideological orientations. A number of game theoretic models demonstrate that the credibility of signals improves as political actors’ preferences converge (Crawford and Sober 1982; Lupia and McCubbins 1994). The first principle of Keith Krehbiel’s information theory of congressional committees, for instance, states that “the more extreme are the preferences of a committee specialist relative to preferences of a nonspecialist in the legislature, the less informative is the committee” (1992: 81). When senders and receivers in incomplete information games share a common world view, the signals conveyed are especially informative. Conversely, as preferences diverge, signals are often indecipherable. If the president is to make an effective case for deploying troops, members of Congress must believe the information he transmits. Shared ideological orientations facilitate belief. All else equal, presidents should garner trust from members of his party, and suspicion from the opposition party. As his party grows in size and strength, therefore, the president ought to benefit from greater legislative discretion (formal and otherwise) to exercise force abroad. Currying Presidential Favor: Presidents can do a number of things to shore up the electoral prospects of members of Congress. By visiting their districts; appearing in their television advertisements; or introducing them to potential funders; presidents can significantly affect members’ electoral returns. Precisely because constituents pay more attention to domestic than foreign policy matters when deciding how to vote, members of 10

Congress often have little to lose, and often much to gain, from actively supporting a president interested in exercising force abroad. Of course, presidents work on behalf of members of their own party. Republican Senators rarely have anything to gain from currying the favor of Democratic presidents; as Democratic Senators have little reason to go out of their way to support Republican presidents. To the extent that broad grants of authority in foreign affairs helps members remain in the president’s good graces, Republican [Democratic] Senators have cause to support Republican [Democratic] presidents when they consider exercising force abroad. While resting upon different first principles, all of these micro-theories generate the same prediction: Senate members of the president’s party will line up behind the president during times of international crisis. But from a logistical standpoint, presidents can deploy the military without first securing congressional approval. Indeed, an ability to strike first and place upon Congress the onus of coordinating a response stands as a defining characteristic of the president’s unilateral powers (Howell 2003). Why, then, should presidents care about whether or not Congress supports a military use of force? How exactly does opposition within Congress constrain the president ex ante? And why must presidents anticipate the strength and source of this opposition, and adjust their military plans accordingly? Again, several plausible explanations arise. Dismantling the President’s Military Venture: Anticipating a large contingent within Congress actively resisting their policies, presidents may be reticent to initiate force. The opposition party within Congress may attempt to dismantle a particularly controversial military campaign, refusing to appropriate needed funds, calling for the return of troops sent on ill-conceived foreign missions, or raising concerns about the efficacy of the intervention. Congress can actively work against the president, materially affecting the course of a military campaign. In their study of the War Powers Act, David Auerswald and Peter Cowhey (1997: 11

523) show that Congress regularly places upon presidents obligations (reporting requirements, budgetary limitations, accounting procedures) that can prove quite burdensome. Having to stave off a mobilized opposition party within Congress during the course of a military campaign may dissuade presidents from initiating force at all. Coalescing Public Opinion: Congress exerts influence over public opinion concerning foreign policy (Lindsay 1992: 3). Whether the issue is defense programs or specific military operations, Congress can “take to the streets,” frame the ensuing debate, and, with varying success, turn public opinion against the president’s preferred foreign policy (H. Smith 1988; Caldwell 1991). If the president anticipates that Congress will push public opinion against him, with regard to the use of force specifically, or against his approval ratings more generally, he may be less likely to engage in the use of force. Dispelling Myths of Political Resolve: A large body of work on crisis bargaining shows that when negotiating with one another, states have strong incentives to conceal their true private preferences (Morrow 1986); further, an inability to credibly reveal these preferences can lead to the breakdown of negotiations and the initiation of war (Fearon 1994). Kenneth Schultz, however, has shown that the existence of an opposition party (which has no incentive “to collude in a bluff”) makes signals sent between states more informative, and hence mitigates the likelihood of military conflict. When Congress supports the president, the president can credibly convey his intentions to follow through on a military venture; but when Congress opposes the president, the president will have a much more difficult time signaling his resolve. “The opposition party can undermine the credibility of some challenges by publicly opposing them. Since this strategy threatens to increase the probability of resistance from the rival state, it forces the government to be more selective about making threat” – and, concomitantly, more cautious about actually using force (1998: 840). The potential for domestic political strife, as such, creates a 12

disincentive for the president: it weakens the credibility of signals of resolve, thereby encouraging bargaining intransigence on the part of rival states. The resulting (higher) likelihood of protracted conflict and its increased cost will lead the president to be wary of such strategies (Smith 1998).2 There are, then, a variety of reasons why members of the president’s party should be more likely to support the president, reasons that trace back to their shared electoral fortunes, the credibility of signals conveyed across the branches of government, and the electoral benefits of currying the president’s favor. So too are there multiple reasons why presidents will anticipate congressional opposition and, possibly, disband planned military ventures, foremost among them being Congress’s ability to directly challenge the president and the associated problems of credibly conveying strong resolve to rival states. The empirical tests that follow do not allow us to evaluate these competing micro-theories, and hence we remain agnostic as to their individual merits. Instead, we test the basic expectation that arises out of all these micro-theories: the partisan composition of Congress should systematically influence the frequency with which presidents exercise force abroad.

Section III: Empirical Tests To test whether congressional politics play a role in the president’s calculus to deploy military troops abroad, we conduct several statistical examinations of the United State’s use of force between 1945 and 1995. Our data draw from Fordham (1998a), Fordham and

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Schultz (2001) builds upon this selection logic, arguing that empirical tests for audience costs are likely to systematically underestimate those costs to state leaders.

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Sarver (2001), and Zelikow (1987), all of which update the original Blechman and Kaplan time series that ended in 1976.3 Blechman and Kaplan ranked demonstrations of force on a five point severity scale. Many scholars use only the most severe uses of force in their analyses, i.e. instances that involved the deployment of nuclear capabilities or the mobilization of multiple aircraft carrier task groups, battalion, or combat wings (e.g., Fordham 1998a, 1998b). This decision, however, is by no means universal (see Mitchell and Moore 2002). Rather than make exclusionary decisions in our own analyses, we initially take three cuts of the force data: all uses, major uses (1-3 on the severity scale), and minor uses (4-5). A priori, one might expect Congress to exert the most influence in major uses of force, but we do not want to dismiss the possibility of broader legislative involvement in foreign policy. To this end, we present results using all three versions of the dependent variable. Figure 1 shows the historical trends of the use of force in U.S. foreign policy.4 Note that there is a general increase in the use of force during the Cold War era, with two major peaks in the early 1960s and mid-1980s. The first peak reflects increased pre-Vietnam War activity in Southeast Asia, multiple crises in the Middle East, as well as the recurrent Berlin crises of the early Kennedy Administration. The 1980s peak largely represents U.S. deployments to the Middle East after the Israeli invasion of Lebanon and increased activity in Central America. To measure congressional support for the president, we compute the percentage of seats held by the president’s party in the Senate and label this variable Percent President Party. We focus on the Senate because of its greater involvement in foreign policy matters; Ironically, the one article that focuses at length on presidential-congressional relations uses the Militarized Interstate Dispute data (MIDS) rather than the traditional use of force data (Gowa 1999). Given the MIDS underreporting of threats to use force, the Blechman/Kaplan data are superior to test theories of U.S. foreign policy. See Fordham and Sarver 2001. 4 Yearly data is used in the graphs simply for purposes of visual coherence. All analyses use quarterly data. 3

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measures that incorporate the House, however, generate comparable, and occasionally stronger, results. Presumably, as the size of the president’s party increases within the Senate, the president should enjoy additional discretion to deploy troops abroad. Conversely, as the opposition party increases in size, the president’s ability to use military force should attenuate.5 Data are aggregated on a quarterly basis. For the major force time series, autocorrelation function plots do not reveal any dynamics, making standard event count models appropriate. A slight dampening dynamic process, however, is observed for the minor and all force time series. Simple event count models, in these instances, may yield inefficient and potentially biased results. Both Poisson autoregressive (PAR) models and general estimation equations (GEE) models allow for corrections of AR processes in time series event count data (Brandt and Williams 2001; Zorn 2000). In this context, the principal difference between these classes of models concerns the structure of the autoregressive process. PAR models isolate and correct for AR processes across an entire time series; GEE models correct for AR processes within clusters of observations. Ultimately, the choice between models is inconsequential, as all yield virtually identical results. For the sake of consistency, therefore, we report for each of the use of force measures Poisson regressions with robust standard errors that account for clustering on each president.6 To account for individual differences in each president’s leadership style, military experience, and policy agendas, all of which may have some bearing on his willingness to 5

We also compute an alternative to the Percent President Party variable based on the “legislative potential for policy change” (LPPC) scores created by Cooper, Brady, and Hurley (1977). These scores use (1) the size of the majority party; (2) the majority party’s internal cohesiveness; (3) the size of the minority party; and (4) its cohesiveness. We modify the scores only slightly, substituting the president’s and opposition parties for the majority and minority parties respectively. This measure generates nearly identical results across all models. In addition, we also estimated models that include a simple indicator variable for divided government. Estimates that are consistent with those reported below arise regardless of whether divided government is defined on the basis of only the Senate majority party or the majority party in both chambers of Congress. 6 The ACF plots and results from PAR and GEE models are available from the authors upon request. Likelihood-ratio tests for each model confirm the appropriateness of Poisson over negative binomial models.

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exercise force, we include intercept variables for each administration. 7 The use of force, then, is assumed to be a function of the partisan composition of Congress and presidential fixed-effects. (1)

FORCE = α + β 1PresidentParty + β iPresident + ε

If our expectations about the relevance of Congress hold, β 1 should be positive and statistically significant. The first three columns of Table 2 present the estimated Poisson regression results on all, minor, and major uses of forces. For two configurations of the dependent variable, congressional-presidential politics do not seem to play a strong role. When using all and only minor uses of force as the dependent variable, Percent President Party is not statistically significant. Major uses of force, however, are affected by domestic political factors, as the partisan composition of the Senate appears to play a significant role in shaping the president’s willingness to deploy troops abroad. The positive coefficients suggest that as the size of the president’s party grows, the president’s freedom to use the military for significant purposes also increases. Although theory suggests that the size of the president’s party affects the ability of the president to use force abroad, it is largely silent with regard to the functional form of the relationship. Upon reflection, however, there is good reason to expect that the impact of Percent President Party will be non-linear. Given supermajoritarian procedures and the powers and privileges associated with becoming the majority party in Congress, increasing the size of the president’s party from 49 percent to 51 percent or from 59 to 61 percent is likely to be more important than an increase from 39 to 41 (Krehbiel 1999). To test for the possibility

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F-tests regularly reject the null that the presidential fixed effects are jointly insignificant.

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of non-linear effects, we add a quadratic term to Model 1 and re-estimate the impacts for each version of the dependent variable. The results are presented in columns 4-6 in Table 2. For the non-linear model estimations, results are now consistent across each version of dependent variable. In all three estimates, the size of the president’s party has a strong impact on the propensity of the U.S. to use force. The signs of the linear and quadratic term suggest a U-shaped functional form. Marginal increases in party strength at the low end of the distribution leads to a slight decline in the use of force; but for marginal party gains at the middle and upper ends of the distribution, the propensity to use force increases more dramatically. For example, given the estimates in column 6, a move from 45 percent to 48 percent for the President’s party yields an increase of 6 percent in the expected total number of uses of force, yet a move from 55 to 58 percent leads to an increase of over 19 percent in the expected count. These predicted effects continue to grow as one increases the size of the president’s party: beginning with 60 percent, a gain of seats resulting in a 63 percent majority produces a 26 percent increase in the expected frequency of conflict. Based upon the estimates in columns 4-6 of Table 3, Figure 2 provides three sets of predicted incident rates. Each graph in Figure 2 is created through the use of statistical simulations (see King, Tomz, and Wittenberg 2000). The vertical lines represent 95 percent confidence intervals around each point prediction. The first panel illustrates the predicted number of major uses of force for different values of Percent President Party. Although the shape of the relationship is quadratic, the influence of seat gains is quite small below the fifty percent mark; thereafter, the slope increases markedly. For all and minor uses of force, there is a steeper decline in propensity to use force for values at the lower end of the spectrum. These differences, however, are small compared to the relative impact of seat gains above the fifty percent threshold. In 17

each case, the minima of predicted values for uses of force lie between 45 and 50 percent. As the president’s party approaches a majority, his freedom of action expands, while gains above and beyond 50 percent yield ever increasing executive autonomy. The substantive meaning of these results is unambiguous: the level of partisan support for the president within the Senate stands out as a major determinant of the U.S. propensity to use force abroad. As discussed in section 2, scholars have focused almost exclusively on other domestic and international factors that shape the president’s ability to use force abroad. In order to ensure our findings are not the result of omitted variable bias, we estimate the following model which incorporates many of the alternative hypothesized influences on the use of force: (2)

FORCE = α + β 1PresidentParty +β 2PresidentParty2 + β 3Unemployment + β 4CPI + β 5Approval + β 6W-Elect + β 7P-Elect + β 8War + β 9ColdWar + β 10Hegemony + β 11WorldDispute + β iPresident + ε

Again, we interchange three measures of FORCE (all, minor, and major) as the dependent variable. Consistent with a burgeoning literature on the political economy of the use of force (Ostrom and Job 1986; Fordham 1998a), we incorporate the quarterly unemployment rate and the inflation rate (CPI), both of which were taken from the Bureau of Labor Statistics. Past research finds that poor economic performance is likely to lead to incentives for the president to act aggressively in foreign policy affairs (James and Oneal 1991; Fordham 2002). Because much of the literature on the use of force draws upon theories of diversionary war, we control for the president’s public approval rating. The impetus for much of the original quantitative work on the subject was Ostrom and Job’s (1986) finding that approval ratings were a highly significant determinant of the use of force – though

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subsequent research has proven less definitive on the matter. We measure the first Gallup approval rating for the president in each quarter. 8 A related body of work examines whether elections usher in additional uses of force (Stoll 1984; Gaubatz 1991). This research contends that “rally around the flag” effects establish incentives for presidents to use force during the months immediately preceding an election, provided that the nation is not already at war. Thus, we introduce two variables, W-Elect and P-Elect. The first is coded “1” during the first three quarters of a presidential election year in which the U.S. is involved in a major war; the second is coded “1” in the first three quarters of the remaining peace-time presidential election years. The next four variables capture facets of the international environment that may impinge on the president’s autonomy in foreign policy. Due to contemporary military commitments, there should be a tendency for presidents to employ force for bargaining purposes less often during times of war. Thus, we create a dummy variable labeled “War”, coded “1” during periods of international wars in which the U.S. was involved (here, Korea, Vietnam, and the Gulf War). The Cold War was also a period of unprecedented concern over international engagement of U.S. forces. To control for its influence on the U.S. propensity to use force, we include a dummy variable coded “1” during the 1945-1989 period. To account for systemic forces that have been linked to the onset of both interstate wars and disputes (Mansfield 1994; Mansfield and Pevehouse 2000), we include a measure of U.S. hegemony during the period of analysis. The measure is the percentage of international military capabilities held by the United States and derives from the Correlates of War Some research, including Ostrom and Job, do not measure approval at the outset of the period of observation, but throughout the period. This specification invites endogeneity problems, as rally around the flag effects emanating from exercises of force may have popularity ratings. In the handful of quarters missing approval data, we fill the data by using a linear interpolation. We also interpolated by using the last known poll. The results are consistent regardless of the method used. 8

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Capabilities data set (Small and Singer 1990). Finally, we include a measure of the number of world military conflicts which begin in each quarter of observation. Presumably, a higher number of world conflicts provides more opportunities for the U.S. to respond with the use of force (Meernik 1994; Fordham 1998a). The data is taken by aggregating non-U.S. militarized interstate disputes (MIDS) over the period of observation.9 As in table 2, all models include presidential fixed effects and are estimated using Poisson regressions with robust standard errors. Table 3 presents estimates across the three measures of force. Consistent with our initial findings, the linear and quadratic terms measuring senatorial support for the president are highly significant predictors of the quarterly number of the use of force regardless of the form of the dependent variable. The distinction between major and minor uses of force, then, appears less important when the influence of Congress is examined. While the marginal effects of senatorial support on the predicted uses of force differ slightly for minor and major uses of force at the lower end of the distribution, on the whole, the effects appear robust. For all three versions of the dependent variable, the linear and quadratic terms generate consistent and significant effects. Similar to the effect of party size on major uses of force in Model 1, increases at lower levels of party size (45 percent to 48 percent) yield smaller increases (roughly 6 percent), than to corresponding increases at higher levels of party size (moving from 55 percent to 58 percent brings an increase in 18 percent in expected count).10 Many of the remaining model estimates also are consistent with previous findings, although some of these congruencies disappear when only major uses of force are evaluated.

The MIDS data ends in 1992. To extend the data until 1995, we performed a comprehensive search for events that seemingly met the MIDS criteria from 1992-1995. For a description of the MIDS data, see Jones, Bremer, and Singer 1996. 10 Figures are based on estimates in column 3 of Table 3. 9

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Specifically, estimates for the economic variables (Unemployment and CPI) mirror the original Ostrom and Job findings that higher levels of “economic misery” correspond with higher levels of military activity (these are also consistent with Fordham 1998a, b). For example, increasing the level of inflation by one standard deviation leads to an increase of 28 percent in the expected count of all uses of force. Yet, when only major uses of force are evaluated, these results weaken significantly. In fact, in the model of major uses of force, the influence of all economic-related variables disappears entirely. The elections variables yield some findings that diverge from previous studies. Some scholars do not differentiate war-time and peace-time elections (Ostrom and Job 1986; Gowa 1998; Meernik 1994). Interestingly, none of those studies finds elections to be significantly related to the use of force. Fordham, who does differentiate elections, finds that war-time elections are significant predictors of the use of major force.11 The models in table 3 indicate that it is peace-time elections that matter, but only with regard to minor uses of force. In these minor force models, the expected count difference increases over 30 percent during peace-time elections. One possible explanation could be that while presidents may want to gain support for foreign policy during an election year, they are unwilling to take large risks to do so and thus confine their activities to military operations involving a single squadron or company of troops. The approval variable never attains statistical significance in any of our estimations, even when including alternative specifications that are not reported here. This is consistent with the findings of both Meernik and Fordham, but counters Ostrom and Job’s claim that lagging approval ratings establish incentives for presidents to use force. Other variables are of the predicted sign – the Cold War has a positive and statistically significant influence on Fordham’s election variables differ from ours. While we isolate the three quarters leading up to the national election, Fordham 1998a isolates all four quarters in the calendar year of an election, as well as the first quarter of the following year when an incumbent is re-elected. 11

21

military activities. Based on the estimates of column 3, the expected number of uses of force more than doubles during the Cold War. Other control variables, such a hegemony and ongoing wars depress the propensity of presidents to deploy U.S. troops, yet their statistical significance varies based on the dependent variable. The level of military hostility in the world appears to have no consistent or statistically significant influence on the propensity of the U.S. to engage the military.12 Given these results, we contend that much of the previous empirical work on the use of force in U.S. foreign policy suffers from omitted variable bias. Without taking account of presidential-congressional politics, as well as fixed presidential effects, both of which clearly impact the use of force, scholars risk excluding a significant determinant of U.S. foreign policy. Moreover, these findings intimate something more fundamental about much of the theory that spawned the literature on U.S. use of force policy – namely, that the same forces that affect prospects for the president’s legislative agenda also determine the discretion of presidents to exercise force abroad. Domestic and Foreign Policy Tradeoffs Increased resources devoted to one policymaking sphere may imply decreased resources available for another. When embroiled in military conflicts abroad, presidents have considerably less time to direct their domestic legislative agenda through Congress; conversely, when freed from foreign military entanglements, presidents can assist an increasing number of laws along the legislative path. If true, we should find evidence of a trade-off between foreign and domestic politics. All else equal, presidents who spend an exorbitant amount of time on domestic policy should be less engaged in foreign military

12

Because the use of force data contains some overlapping uses of force (different operations during the same calendar period against the same target), we re-estimated all models removing the overlapping observations. The resulting estimations are nearly identical to those presented here.

22

ventures; meanwhile, presidents who stake their legacies on military initiatives should fail to enact large numbers of significant laws. To test this claim, we add one independent variable to equation 2: the number of “non-trivial” laws enacted each quarter. Non-trivial laws encompass all “landmark,” “important,” and “ordinary” laws enacted each Congress. Landmark enactments consist of the “Sweep One” laws identified in David Mayhew’s Divided We Govern (1991). By measuring the amount of coverage laws received in the New York Times, the Washington Post, and the annual Congressional Quarterly almanacs, Howell et al (2000) categorized all of the remaining laws as important, ordinary, or trivial. Between 1945 and 1995, 17,830 total laws were enacted, 1 percent of which were deemed landmark, 1 percent important, 10 percent ordinary, and 87 percent trivial.13 We focus exclusively on uses of major force, which demand from presidents more attention and resource commitments. These demands should intensify the trade-off between domestic and international policies, leading to a negative correlation between the passage of non-trivial laws and the use of force. The first column of table 4 presents the results. The number of non-trivial laws enacted each quarter has a positive and statistically significant relationship with the number of uses of force – exactly the opposite of what one would expect given a theory positing a tradeoff between domestic and international politics in presidential decision-making.14 Moreover, Percent President Party retains its sign and statistical significance.

13

Howell et al 2000 used these count data to test the hypothesis that Congress enacts fewer important laws during periods of unified than divided government. They find that while divided government depressed the number of landmark laws enacted, it has no effect on the number of important and ordinary enactments, and has a positive effect on the number of trivial laws passed each Congress between 1945 and 1994. For the analyses conducted for this paper, the time series is updated through 1995. 14 The impacts of Percent President Party on all and minor uses of force are statistically insignificant.

23

This model lends no support for the notion that presidents must choose between foreign and domestic policy initiatives. Quite the contrary, increased legislative activity seems to imply greater freedom for presidents to exercise military force abroad. An institutional theory of presidential-congressional relations helps explain why. When the president enjoys strong support in Congress, he is less constrained in both foreign and domestic policy. Stronger congressional support leads to a comparatively easier road for the president to pursue his legislative agenda, just as it affords greater discretion to send troops abroad. Tradeoffs between domestic and foreign policy should be less [more] acute when the president enjoys strong [little] support in Congress. The very institutional structures that support the enactment of numerous laws – namely, widespread support within Congress for the president – also lend the chief executive considerable discretion to exercise force abroad. As a further test of this conjecture, we estimate a set of Seemingly-Unrelated Poisson models, with the use of major force and enactment of significant laws as the two dependent variables.15 As with the use of force, our theory does not anticipate the functional form the relationship between presidential strength and the passage of laws will take. Thus, one set of estimates (table 4, column 2) contains only a linear term of Percentage President Party, while the other set (table 4, column 3) contains both a linear and quadratic term. Even when controlling for the correlated error terms across equations, congressional support for the president is statistically significant, although its functional form differs. In column 3, neither the linear nor the quadratic measure of Presidential power is significant, yet alone, the linear term is highly signifi cant. Larger values for Percentage President Party lead to the enactment of more non-trivial laws and the initiation of increased numbers of military ventures. Congressional support or opposition for the president appears to significantly impact domestic and foreign policy. 15

As in all previous models, both the Force and Laws equations include presidential fixed-effects.

24

Relations between Congress and the president have immediate consequences for both the lawmaking process and the commitment of American troops abroad. The same underlying forces that facilitate lawmaking also lend presidents greater autonomy to use military force. While trade-offs between domestic and foreign policy may exist at the margins, their influence appears to be overwhelmed by the institutional foundations of executive-legislative relations.

Section IV: Conclusion For too long, the use of force literature has ignored domestic political institutions. Indeed, most research equates domestic politics with election cycles, public opinion, and the state of the economy, and nothing more. Finding that presidential public approval ratings are unrelated to the use of force between 1953 and 1978, Moore and Lanoue offer the sweeping conclusion that “international politics, not domestic politics, [must be] the primary determinant of conflictual U.S. foreign policy behavior” (forthcoming). Because it is not an integral component of the domestic politics of international engagement, Congress, presumably, does not need accounting for. We argue otherwise and show empirically that Congress is a key determinant in the president’s proclivity to use force. On the whole, we find a strong, non-linear correlation between the composition of Congress and the frequency with which presidents use force abroad. This relationship holds for all use of force time series, though the effects are clearest with regards to major deployments. As their party’s share of the Senate increases, presidents conduct military campaigns abroad with increasing frequency. Conversely, as the size of the opposition party increases, presidents act with force less and less often. This finding is robust across various model specifications and using multiple operationalizations of congressional support. Moreover, our findings cast doubt on the 25

conjecture that presidents face a zero-sum tradeoff between foreign and domestic politics. Quite the contrary, the same factors that facilitate the passage of the domestic agenda will facilitate the use of force as well. The larger the support of the president in the Senate, the more likely are major uses of force and more likely is the passage of important pieces of legislation. Further, it appears that many of the prior conclusions regarding the influence of public opinion, elections, and the state of the economy may suffer from omitted variable bias. For scholars, the proper question should not be whether domestic political institutions, on the whole, matter. Rather, the challenge is to specify exactly when they matter, exactly how their constraining influence manifests, and what this entails for the ultimate conduct of American foreign relations. In future research, scholars would do well to study the particular causal mechanisms that allow Congress to influence foreign policy. Moreover, these mechanisms may influence the choice of foreign crises presidents respond to, the timing, scope, and duration of the response, and the terms of the conflict’s ultimate resolution. This paper establishes a preliminary point of departure. While the president certainly commands considerable discretion to exercise force when, and as, he pleases, Congress remains a force to be reckoned with. In the conduct of foreign military relations, as in most every other area of public policy, Congress often wields significant influence over presidential decision-making.

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(A) Major Uses of Force per Year

(B) Minor Uses of Force per Year

8

14 12

6

10 8

4 6 4

2

2 0

0 1945

1955

1965

1975

1985

1995

1975

1985

1995

1945

1955

1965

1975

1985

1995

(C) All Uses of Force per Year 22 20 18 16 14 12 10 8 6 4 2 0 1945

1955

1965

Figure 1: U.S. Use of Force, 1945-1995 NOTE: Graphs use annual counts and present a non-linear smoother for visual coherence.

27

(A) Influence of Presidental Party Support on Major Uses of Force

(B) Influence of Presidental Party Support on Minor Uses of Force

Expected Minor Uses of Force

Expected Major Uses of Force

3

2

1

0

3

2

1

0 0.350

0.500 Proportion of Seats in President's Party

0.600 0.625

0.350

0.500 Proportion of Seats in President's Party

0.600 0.625

(C) Influence of Presidental Party Support on All Uses of Force

Expected All Uses of Force

5

4

3

2

1

0 0.350

0.500 Proportion of Seats in President's Party

0.600 0.625

Figure 2: Predicted Force Counts Note: Vertical Lines are 95% confidence intervals, based on simulations 28

Table 1. Descriptive Statistics. Variable Dependent Variables Major Force Minor Force All Force Independent Variables Pct. President Party in Senate CPI Unemployment Approval Election Year (War) Election Year (Peace) War Cold War Hegemony Non-trivial Laws Passed

Mean

Std Dev.

Min.

0.7 1.2 1.9

0.9 1.2 1.5

0 0 0

0.52 4.4 5.6 54.9 0.06 0.12 0.26 0.88 0.34 12.2

0.09 3.7 1.7 13.7 0.24 0.32 0.44 0.32 0.06 11.3

0.35 -2.7 1.1 23.0 0 0 0 0 0.26 0

Max. 5 5 7 0.68 18.9 10.7 87.0 1 1 1 1 0.52 56

N = 204 for each variable

29

Table 2. Poisson Estimates of Uses of Force by the United States: 1945-1995. All Force

Minor

Major

Percent President Party

0.473 (2.796)

-1.179 (3.928)

2.717** (1.212)

(Percent President Party) 2

--.--

--.--

Constant

0.629 (1.497) 204

N=

All Force

Minor

Major

-32.072*** (6.661)

-42.380*** -18.704** (9.424) (7.747)

--.--

34.318*** (8.563)

43.094*** 22.813*** (12.016) (8.439)

1.087 (2.086)

-1.643** (0.656)

8.120*** (1.128)

204

204

204

10.685*** 3.213* (1.672) (1.732) 204

204

** = p < .01; * = p< .05; one-tailed tests. Note: Each model is estimated using Poisson regression with Huber/White/sandwich clustered standard errors. Each model also contains fixed effect terms for each Presidential administration, which are not reported to conserve space.

30

Table 3. Poisson Estimates of Use of Force by the United States: 1945-1995. All Force Percent President Party

Minor

Major

-26.948*** (2.021)

-34.951*** (6.380)

-18.270* (10.184)

(Percent President Party) 2

30.306*** (2.546)

37.564*** (7.532)

22.228** (11.306)

Unemployment

0.152*** (0.036)

0.170*** (0.046)

0.119 (0.089)

CPI

0.054** (0.025)

0.067*** (0.022)

0.027 (0.040)

Approval

-0.0004 (0.007)

0.001 (0.008)

-0.004 (0.008)

War-time Election

0.127 (0.229)

-0.010 (0.303)

0.401 (0.264)

Peace-time Election

0.287** (0.119)

0.425*** (0.067)

-0.038 (0.271)

Ongoing War

-0.501*** (0.177)

-0.587*** (0.186)

-0.377 (0.256)

Cold War

0.477*** (0.069)

0.152* (0.090)

0.794*** (0.142)

Hegemony

-2.912* (1.625)

-4.453* (2.376)

-0.334 (3.236)

World Disputes

-0.004 (0.020)

0.011 (0.034)

-0.023 (0.025)

Constant

6.321*** (0.859)

8.211*** (1.689)

2.771 (2.559)

N=

204

204

204

*** = p < .01; ** = p < .05; * = p< .10; two-tailed tests. Note: Each model is estimated using Poisson regression with Huber/White/sandwich clustered standard errors. Each model also contains fixed effect terms for each Presidential administration, which are not reported to conserve space.

31

Table 4. Poisson Estimates of Use of Force Controlling for Legislative Activity: 1945-95. MAJOR FORCE

____

DV: USE OF FORCE Percent President Party

-17.723* (10.545)

-18.270* (10.184)

-18.270* (10.184)

(Percent President Party) 2

21.546* (12.086)

22.228** (11.306)

22.228** (11.306)

Unemployment

0.111 (0.072)

0.119 (0.089)

0.119 (0.089)

CPI

0.030 (0.036)

0.027 (0.040)

0.027 (0.040)

Approval

-0.001 (0.007)

-0.004 (0.008)

-0.004 (0.008)

War-time Election

0.461** (0.223)

0.401 (0.264)

0.401 (0.264)

Peace-time Election

-0.007 (0.312)

-0.038 (0.271)

-0.038 (0.271)

Ongoing War

-0.517* (0.302)

-0.377 (0.256)

-0.377 (-0.256)

Cold War

0.798*** (0.118)

0.794*** (0.142)

0.794*** (0.142)

Hegemony

-0.750 (2.896)

-0.334 (3.236)

-0.334 (3.236)

World Disputes

-0.024 (0.027)

-0.023 (0.025)

-0.023 (0.025)

Laws Passed

0.020** (0.008)

--.--

--.--

Constant

2.584 (2.347)

2.771 (2.559)

2.771 (2.559)

Percent President Party

--.--

1.274** (0.592)

-9.006 (7.344)

(Percent President Party) 2

--.--

--.--

10.813 (8.161)

Approval

--.--

-0.007 (0.005)

-0.008 (0.006)

DV: LAWS PASSED

32

Table 4 (con’t) MAJOR FORCE DV: LAWS PASSED (con’t) War-time Election

--.--

-0.109 (0.112)

-0.072 (0.140)

Peace-time Election

--.--

-0.144 (0.228)

-0.150 (0.234)

Ongoing War

--.--

0.250 (0.161)

0.267 (0.175)

1.589*** (0.375)

4.033** (1.831)

204

204

Constant N=

204

*** = p < .01; ** = p< .05; * = p < .1; two-tailed tests. Note: Each model is estimated using Poisson regression with Huber/White/sandwich clustered standard errors. Each model also contains fixed effect terms for each Presidential administration, which are not reported to conserve space.

33

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