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Since President Truman’s “police action” in the Korean War, scholars in law and political science have considered the possibility that presidents would attempt to substitute congressional authorization with authorization from an international organization when using military force. While presidents have on multiple occasions appeared to do so, after considering the scale of the operations undertaken there is clear evidence that presidents since Truman have avoided major war absent formal congressional approval. Instead, uses of force undertaken with mere international approval have consistently been orders of magnitude smaller in scale than those conducted pursuant to formal authority from the legislature.
Presidents have an extensive history of obtaining international approval to use force while simultaneously neglecting to receive a congressional authorization for use of military force (AUMF) for the same operation. Truman’s decision during the Korean War is perhaps one of the most well-known examples, but the practice has continued over more recent history. During the Cuban missile crisis, President Kennedy acquired express approval from the Organization of American States to “quarantine” the island but did not actually obtain a true AUMF from Congress for his actions—which included the potential of thermonuclear war. More recently, U.S. deployments to Somalia in the early 1990s were approved by a resolution of the U.N. Security Council, but congressional authorization was received only after the disastrous Battle of Mogadishu (which included the well-known “Black Hawk Down” incident) and essentially was a requirement to leave the war-torn nation. Deployments to the Balkans in the 1990s likewise came under the approval of the United Nations but lacked domestic authorization, and the Kosovo intervention was authorized by NATO—as Russia vetoed any attempt to secure U.N. authorization—but Congress narrowly rejected an AUMF. President Obama continued this trend when he did not seek permission from Congress for the 2011 Libya intervention, which received the approval of the United Nations and the Arab League.
One point of contention in the war powers debate among legal academics has been the relationship between international and congressional force authorizations. While any use of force can be analyzed for its legality separately under both constitutional law and international law, the two areas of law do not operate completely independently of one another. Bradley and Galbraith demonstrate this dynamic through pathways such as international law’s formal influence on domestic legal doctrine and the transfusion of American domestic interpretive principles into U.S. understandings of international law. In the use-of-force context, the executive branch has often cited U.N. Security Council resolutions as part of its constitutional justification—in Somalia, Haiti, Bosnia and Libya, for example. Most notably, however, was the constitutional justification put forth by the executive branch for the Korean War, which argued that “it was appropriate to use force to support the Security Council’s resolutions because the ‘continued existence of the United Nations as an effective international organization is a paramount United States interest’” and, furthermore, that the “U.N. Charter triggered the President’s obligations and authority under the Take Care Clause.” As a major conflict in which nearly 40,000 Americans died in combat, the Korean War has served as an often-cited precedent for expansive views of the power of the president to use force absent formal congressional authorization.
Among lawyers there is still disagreement as to exactly when the United States can use force with international approval while lacking congressional authorization—with some preferring Congress to always have a say and others arguing that presidents should be able to act without Congress to enforce international resolutions. In the middle of these two extremes, there seems to be a weak consensus that major wars require congressional consent, while smaller uses of force can sometimes be launched unilaterally. This is consistent with many of the more recent Office of Legal Counsel (OLC) opinions, which state that uses of force absent congressional approval are constitutional when the “‘anticipated nature, scope and duration’ of the conflict [does not] rise to the level of a war under the Constitution.” However, some OLC opinions have taken an even more expansive view of the presidential power to wage war, and the attorney general and president always have the authority to supersede the legal test set forth by the office.
Political scientists, likewise, have also taken note of the relationship between congressional and international force authorizations. Scholars of international relations have recently given attention to the effect international authorizations have on domestic public opinion regarding the use of force. Chapman, for example, argues that U.N. Security Council resolutions can serve as a credible signal to domestic constituents that a contemplated use of force is a wise idea. Presidents have an incentive to ask the U.N. for approval because of such a boost in public opinion, and they risk a relatively small downside in the event approval is not forthcoming because the administration can discount the international organization as being biased against U.S. interests.
Recent political science scholarship has argued further that presidents can use international authorization as a substitute for congressional approval. Kreps, for example, convincingly demonstrates that presidents will often attempt to use legitimizing rhetoric to strengthen an otherwise weak legal position—acting as an advocate not in a court of law but most certainly in the court of public opinion. Kreps distinguishes between “legality”—having formal congressional approval—and “legitimacy,” and argues that if the former is absent for a given intervention, the president can make up for this by appealing to other types of authority. While in earlier periods of U.S. history presidents had to rely on alternative strategies of legitimization, since the proliferation of international institutions after World War II, presidents have been able to use authorizations from international organizations in lieu of authorizations from Congress. The historical record seems to support the plausibility of this argument. Indeed, many American combat operations in recent memory have fallen into this category—including many uses of force during the Clinton and Obama administrations.
Thus, as Kreps notes, presidents have often cited international legal authority when congressional approval was lacking. Other scholars have likewise found that congressional and international approval cause similar boosts in public support for the use of force. If anything, a signal of support from an international organization might be seen as more credible than that of Congress, given that the voting members would theoretically be less biased than members of Congress—as Franck and Patel argue, the Security Council is “far less likely to be stampeded by combat fever than is Congress.” When all U.S. uses of force over the past 120 years are taken into account, though, it is apparent that the scale of operations undertaken with only international authorization are clearly of a different sort than those undertaken with congressional approval.
The figure above plots U.S. uses of force over time—as defined by the Correlates of War Project’s dataset of Militarized Interstate Disputes (MIDs)—by the number of U.S. combat deaths suffered in each engagement. When casualty figures were missing from the dataset or differed substantially from other public sources, the most well-recognized source was used. Note that the MIDs dataset includes only interstate disputes and ends in 2010, so four additional uses of force—Somalia in 1992-1993, the 2011 Libya intervention, and cruise missile strikes against Syria in 2017 and 2018—were added to the figure above. Points in red are those uses of force that received formal congressional approval, while green points are those that had no such authorization from the legislature but were conducted under the approval of an international organization. While the United Nations has been the most common forum for approval, presidents have often cited approval from other international organizations when the authorization of the United Nations has been lacking. Note that if a use of force had both international and congressional approval—the 1991 Gulf War, for example—it is shown in red.
When classifying uses of force based on the scale of the operation (based on U.S. fatalities, above, or on the level of escalation, below), a clear pattern emerges. Since the Korean War set a precedent that subsequent presidents consciously sought to avoid, major uses of force have been undertaken only with the formal backing of the legislature. For smaller operations, however, presidents have consistently been willing to use force absent congressional authorization—most paradigmatically in cases of obvious self-defense or the protection of Americans abroad. Humanitarian interventions have often been undertaken under the auspices of an international organization—and these deployments are all orders of magnitude less lethal than the major uses of force undertaken with congressional approval.
Short-Term Public Support Versus Long-Term Commitment
If it is the case that presidents are willing to consider using force unilaterally and, furthermore, if international authorizations serve the same signaling function to the public that congressional authorizations do, what explains the clear disparity in the scale of congressionally versus internationally approved uses of force? One possible explanation is that congressional authorizations actually serve two functions: to boost public support in the short term and to commit members of Congress who voted to authorize force to support the effort further into the future. While international and congressional authorizations both cause similar boosts in public opinion in the short run, only congressional approval has an additional long-run commitment mechanism simply lacking in international authorizations. Political scientist Douglas Kriner has found that members of congress who voted to authorize a use of force are significantly less willing to vote to curtail or publicly criticize an operation later in time. Because legislative measures and public criticism of uses of force are among Congress’s most potent tools in influencing the military deployment decisions of the president, securing congressional approval from the outset helps maintain congressional and public support over the long term. In contrast, the approval of the United Nations, or any other international body, lacks any analogous commitment function; voting members of the U.N. have no comparable “skin in the game” or relevant political influence in U.S. domestic politics after authorizing war. U.S. presidents since Truman have thus all realized that it is politically untenable to risk major conflict absent congressional backing.
Lyndon Johnson, for example, clearly recognized the commitment function of formal congressional authorization. When he asked for support for the Gulf of Tonkin Resolution in 1964, he expressed his belief that “Truman had erred in failing to ask Congress for approval” despite strong congressional support for the Korean War at the outset and that “only if Congress was in on the takeoff would it take responsibility for any ‘crash landing’ in Vietnam.” Historian Michael Beschloss writes that when the war began to escalate in 1965, Johnson noted that “[h]e had asked for the Tonkin Resolution ... because he knew that members of Congress would ‘run when the going gets tough’ and wanted them ‘tied, bound and delivered beforehand.’”
George H.W. Bush specifically encountered the opportunity to use force unilaterally in the Gulf War with U.N. approval but decided against it because of the anticipated high costs despite simultaneously claiming that congressional approval was not legally necessary, continuing the consistent practice of presidents since Truman. The White House counsel wrote that the action could be legally justified absent congressional approval, but that formal authorization would be beneficial both to gain public support and to share responsibility for a possible poor outcome. Secretary of State James Baker advised that it would “be a big mistake to undertake a war as big as this without first securing a resolution of support from Congress.” Bush also specifically noted that while success was likely if public support remained high, failing to get congressional approval might lead to a quick erosion of support after the war began. Thus, Bush ultimately asked for formal congressional support for the Gulf War—despite preexisting U.N. approval—and launched Operation Desert Storm only after such a formal authorization had been obtained.
Even an event that technically had only international approval—the blockade of Cuba in 1962—shows the logic of the argument that presidents undertake operations with a high risk for large-scale bloodshed only when they are confident of congressional approval. Instead of trying to “go around” Congress by appealing to the Organization of American States during the Cuban missile crisis, Kennedy was highly conscious of Congress’s likely response during the crisis and was under enormous political pressure from Republicans and Democrats alike to act forcefully. Indeed, Kennedy’s foremost worry was that Congress would punish him for not doing enough. Furthermore, Congress had provided the administration clear signals before—and during—the crisis that it supported a hawkish response to the developments in Cuba. A few weeks before the October crisis, Congress passed a formal resolution by overwhelming margins stating:
That the United States is determined to prevent by whatever means may be necessary, including the use of arms … in Cuba the creation or use of an externally supported military capability endangering the security of the United States[.]
A formal war authorization had been blocked by Kennedy’s own co-partisans, who had feared escalation before the crisis itself. Moreover, when Kennedy briefed congressional leaders on Oct. 22—during the infamous “13 days”—Republicans in Congress demanded stronger action, including kinetic operations against the missile sites in Cuba, instead of just a blockade. Thus, there was no doubt during the crisis that Congress would support a strong response to the Soviet provocation. It was the brevity of the crisis—and not some legitimating force of an Organization of American States authorization—that made informal congressional support sufficient in October 1962. It is in long, bloody engagements that formal congressional commitment is needed, while in brief encounters informal support can be sufficient due to the smaller threat of political abandonment in the short time period.
While members of Congress have the clear ability to help (or hurt) a war effort in the future, either through public support or through funding decisions, representatives making voting decisions in an international body have no comparable long-term ability to support (or oppose) the war effort. Thus, while both congressional and international authorizations influence public opinion at the outset of a use of force, international authorizations lack the commitment mechanism provided by formal congressional authorization. Because of this, presidents will continue to be unwilling to enter major conflicts without Congress’s authorization, and international approval will be limited to a distant secondary function of boosting short-term claims of legitimacy among the public and international allies. International authorizations may serve as a complement to congressional approval, but they are no substitute.