The separation of powers regarding the use of the military force is one of the most widely disputed issues in the constitutional law of U.S. foreign policy. Many scholars have debated this question from a legal perspective, arguing whether the president or Congress has the ultimate right to control the use of force.(1) Unfortunately, we have little knowledge about the factors that might encourage cooperation or conflict between the president and Congress during real decision-making situations. This is not just a theoretical issue. Undeclared wars are far and away the norm in U.S. history(2), and disputes over the proper division of labor between the executive and the legislature have steadily strengthened the hand of the president in this area. However, since the Vietnam War, Congress has shown itself to be a more assertive actor in foreign policy(3), although it has never successfully used the War Powers Resolution (WPR) to prevent a military action.(4) Understanding "war powers as we live them"(5) can shed some light on the ability of the United States to effectively, responsibly, and democratically wield military power as a tool of foreign policy. To be credible, threats, like promises, must be ratified via domestic processes and to the extent that Congress influences--whether tacitly or explicity--the ratification process,(6) and thus the international bargaining power of the president, we need to understand its behavior.
Since presidents tend to dominate decision making over the use of force, our attention should focus on the response of Congress. Indeed, the WPR places the burden of confronting the president on members of Congress, who must vote to invoke the resolution while presidents have consistently refused to acknowledge the WPR as a check on their powers over the use of force. If Congress fails to vote to invoke the WPR or to otherwise restrain the executive, then the president can draw upon his powers as commander in chief to authorize a fairly wide variety of military operations with little or no regard (at least at the time of the deployment) for legal questions over the matter. Other factors, such as the "rally 'round the flag effect" during times of crisis,(7) also help tilt the balance of power in favor of the president. Finally, U.S. courts have effectively refused to get involved in disputes over the use of force. Unable to objectively define which types of military operations (rescue missions, peacekeeping, UN operations, humanitarian missions, acts of anticipatory self-defense) should invite congressional involvement, the courts have understandably opted to treat the question of executive or legislative supremacy as a political matter, not a legal one.(8) In the view of the courts, Congress has various powers to influence executive military operations; if legislators have not always chosen to employ those powers, the courts can do little about it.
Hence, this article focuses on the behavior of Congress vis-a-vis the president. If the past decade is any indication, there will be repeated opportunities for executive-legislative confrontation over this area of foreign policy. The end of the cold war has seen a number of foreign crises that provoked national debates over the proper role of military force in U.S. foreign policy. These debates seem to have intensified this belligerent attitude on the part of Congress. The question of whether to make these deployments has been especially difficult without the Soviet presence as an organizing principle for decision making in world politics. Debates have been taking place in an ideological vacuum, as neither Democrats nor Republicans have forged compelling rationales for the deployment of U.S. troops, even for peacekeeping or humanitarian missions.
Indeed, one irony of American unpreparedness for a post-cold war future is the spectacle of lawmakers proving unable (or unwilling) to find common ground regarding the use of force during crises such as Iraq's invasion of Kuwait, violence in Haiti, or ethnic conflict in the former Yugoslavia. …