Congress Executive Branch Foreign Relations & International Law

War Powers Reform, U.S. Alliances, and the Commitment Gap

Patrick Hulme, Matthew Waxman
Wednesday, July 5, 2023, 8:01 AM
The history of the War Powers Resolution shows that tighter congressional checks on presidential use of force and strong alliance commitments may be irreconcilably in tension.
Former President Richard Nixon speaks with the U.S. First Infantry Division at their headquarters in Di An, July 1969. (Manhhai,; CC BY 2.0,

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This November will mark the 50th anniversary of the War Powers Resolution (WPR), passed in the aftermath of the Vietnam War over the veto of Richard Nixon. The statute itself has been analyzed ad nauseam over the past five decades. Much focus has been on assessing post-1973 compliance (or lack thereof) with the act, and in recent years there has been intense debate among policymakers, scholars, and commentators about whether and how to reform it

Concurrent with contemporary debate over WPR reform are discussions of whether and how to revitalize U.S. alliances. President Donald Trump called alliances, including NATO, into question. The former president even threatened to leave the pact, while Congress attempted to signal its support for these international commitments via proposed legislation that would require congressional approval of any effort to withdraw from NATO. Focus on the Atlantic alliance has also grown since Russia’s invasion of Ukraine in 2022, and the Biden administration has emphasized the centrality of alliances in U.S. strategy for confronting China. Notably, many of the same commentators who supported strengthening American alliances are the same voices arguing for tightening the president’s war powers.

These two debates—one over reforming the WPR, the other over alliances—are perhaps seen as distinct, albeit related. War powers and alliances, however, are more than just adjacent discussions: They are fundamentally intertwined and, perhaps, irreconcilably in tension with one another. To understand why, it is helpful to look back at the history leading up to the WPR.

Commitment: A Fundamental Problem in the War Power-Alliances Relationship

A basic tension exists between alliances and constitutional checks on the power to enter or initiate armed conflict. The foundational purpose of American alliances from the late 1940s onward has been deterrence. Prior to the Cold War, U.S. alliances were formed during war to win those fights, but after 1945 the purpose was to prevent conflict. Theorist of deterrence Thomas Schelling argued that effective deterrence requires commitment. States can credibly convey what they will do in a tough situation by tying their own hands. Extended deterrence—convincing one’s allies and adversaries that you will show up to defend another state—requires effectively backing oneself into a corner. Schelling even specifically emphasized the importance of a commitment being “automatic.”

Besides the primary goal of deterrence, a credible U.S. commitment to defend allies was important to reassuring them. This was important not just for their benefit, but to prevent destabilizing rearmament or hedging by skittish partners. Because the United States was, and remains, the primary security guarantor in all of its alliances, reassurance requires especially credible commitments; otherwise, partners will pursue alternative strategies to ensure their own defense and survival. 

“Automatic” commitment, however, is just what the Senate sought to avoid when ratifying American mutual defense treaties in the late 1940s and 1950s. Indeed, the language found in U.S. defense treaties that their “provisions [be] carried out by the Parties in accordance with their respective constitutional processes” was included precisely to assuage the fears of senators on this issue. In terms of constitutional powers, a firm commitment to defend an ally undermines control that Congress may claim and seek to later reserve for itself in deciding whether the United States goes to war. 

There are several practical reasons a principled legislator might seek to eschew firm alliance commitments in international politics, including fears over  free-riding or entrapment by allies. Less noble incentives should not be overlooked, though: Lawmakers are often driven by a desire to avoid blame. By avoiding an ironclad commitment today, a member of Congress can avoid political repercussions tomorrow. They can effectively dodge responsibility and allow the executive alone to assume the full political risk entailed by armed intervention in defense of an ally. 

What this means, however, is that Congress’s own desire to avoid firm commitments comes into conflict with effective deterrence and reassurance. Former Secretary of State Dean Acheson noted in his memoirs, for example, that when it came to negotiating NATO, it “became a contest between our allies, seeking to impale the Senate on the specific, and the senators, attempting to wriggle free.”  

A “commitment gap” is thus created between the level of commitment needed for effective deterrence and reassurance—goals well supported and desired by Congress, one should note—and the level of commitment actually provided by an alliance treaty that leaves open the question of the president’s authority to defend allies. In theory, there are several ways to help close this gap. Perhaps the most straightforward solution would be for Congress itself to enhance commitment, for example, by making clear that alliance treaties directly confer authority on the president to use force or by enacting open-ended force authorizations that do so. Failing this, it then falls on the executive branch to convince allies and adversaries the United States will fulfill its obligations without formal action by Congress—which is essentially what happened. One technique is “tripwires”—deployments of U.S. forces on or near an ally’s territory that would virtually guarantee a response (including from Congress) if attacked or threatened. Another possibility is for the presidency itself to develop a reputation for imperialism—in other words, a perceived willingness and ability to act unilaterally. Lastly, the United States could simply scale back its alliance commitments. One way or another, the commitment gap is a vacuum that will be filled or closed.

The Origins of the War Powers Resolution—The National Commitments Resolution

In the early years of the Cold War, as the United States established a network of regional and bilateral alliances with states in the Western Hemisphere, Europe, and the Asia-Pacific, presidents largely resorted to bridging this commitment gap not only with force deployments as tripwires but also with a combination of unilateral diplomatic assurances and broad assertions of presidential power to use force. There is clear evidence, for example, of administrations in the 1950s privately asserting such a power to allies in virtually every alliance: NATO; Korea-U.S.; Sino-American; U.S.-Philippine; Australia, New Zealand, and U.S.; and the Southeast Asia Treaty Organization (SEATO). In other words, prior to the Vietnam War, the commitment gap to U.S. allies was recognized and resolved through assurances and exercises of unilateral presidential power.

Of course, the most high-profile debates over the distribution of the war powers occurred during the war in Vietnam and resulted in the 1973 War Powers Resolution. Although serious legislative efforts to legally reform the allocation of war powers began in 1970 after Nixon’s incursion into Cambodia, the National Commitments Resolution (NCR) of 1969 laid the foundation for these new war powers proposals. That resolution expressed the sense of the Senate that a national commitment to use the armed forces to protect an ally or partner could result “only from affirmative action taken by the Executive and Legislative branches of the United States Government by means of a treaty, statute, or concurrent resolution of both Houses of Congress specifically providing for such commitment.”

The resolution sought to push back on multiple forms of presidential unilateralism, to include not only executive agreements and policy pronouncements made with partner-states lacking a formal alliance with the United States, but also military actions justified by the executive branch as pursuant to formal alliance relationships but perceived as going beyond Congress’s intent. The discussion below focuses on the latter. A 1967 Senate Foreign Relations Committee (SFRC) report regarding the proposed NCR, for instance, gave special attention to the ratification of the North Atlantic Treaty in 1949 and complained of actions taken by the White House in pursuit of alliance reassurance—for example, Truman’s decision to send American divisions to Europe in 1951, the 1962 Rusk-Thanat declaration (which assured Thailand the United States would come to the nation’s defense via its SEATO obligations even if other allies balked), and the Lyndon B. Johnson administration’s claims that SEATO authorized presidential military intervention in defense of South Vietnam. Members of Congress expressed similar sentiments in the 1967 SFRC hearing on the resolution. Chairman J. William Fulbright, for example, specifically criticized statements made by the Eisenhower administration to the effect that the U.S.-Philippine alliance entailed an automatic U.S. response. Thus, the passage of the NCR involved a perception within that Senate that alliances were contributing to an imperial presidency. Notably, the NCR itself seemingly allowed for the possibility of a treaty alone authorizing the use of force as a matter of domestic law, but only if such an agreement “specifically provid[ed] for such commitment.”

Crafting a Legally Binding War Powers Bill

While the NCR was merely a sense-of-Senate measure, its influence would live on via the WPR. The first WPR draft proposed in the Senate in 1970, for instance, specifically utilized the language of the NCR in allowing for the use of force without further authorization if the president acted pursuant to “[n]ational commitments ‘resulting exclusively from affirmative action taken by the executive and legislative branches of the U.S. government through means of a treaty, convention, or other legislative instrument[.]’” 

But by the next year, several prominent senators introduced their own versions of a war powers bill, and many disagreed over whether treaties of alliance alone could empower the president to use force in defending allies. In the process of creating a single compromise bill, the majority position (most prominently found in Sen. Thomas Eagleton’s version of the bill) with regard to treaties was adopted: They would not serve as a sufficient legal basis for the use of force. The final WPR went so far as to state in Section 8 that “[a]uthority to introduce United States Armed Forces into hostilities … shall not be inferred … from any treaty heretofore or hereafter ratified unless such treaty is implemented by legislation specifically authorizing the introduction of United States Armed Forces into hostilities.”

The possible effect of the WPR on treaty obligations and their operation was clearly recognized and debated by members of Congress. In a 1972 floor debate, Sen. Barry Goldwater warned that the bill would create “a complete tie-up in at least 17 treaties.” Another senator similarly argued that the resolution would “severely limit our credibility with our allies.” Other senators, however, held that no commitment was being undermined because nothing was being changed. Sen. Jacob Javits argued that the U.S. and its allies had only committed in their defense treaties to meet threats “in accordance with their respective constitutional processes.” 

The Senate report for the 1973 version of the bill would explain:

[T]he provisions [of the WPR] with respect to treaties are important so as to remove the possibility of future contention such as arose with respect to the SEATO Treaty and the Vietnam war. Treaties are not self-executing. They do not contain authority within the meaning of section 3 (4) to go to war. Thus, by requiring statutory action, in the form of implementing legislation or an area resolution of the familiar type, the War Powers Act would perform the important function of defining that elusive and controversial phrase “constitutional processes” which is contained in our security treaties.

In other words, the WPR’s architects recognized the commitment gap and expected that Congress might address it legislatively, as discussed below.

This created a more practical problem in the meantime, however: How would U.S. allies react to this? Eagleton specifically argued that the WPR would have no effect because U.S. allies had already assumed that Congress would have to formally authorize the use of military force in their defense. The Nixon administration, by contrast, emphasized this specific concern of alliance credibility and often used it as an argument against a WPR. Nixon’s veto message of the WPR in 1973 argued that “the confidence of our allies in our ability to assist them could be diminished” by the resolution. Internal documents show the administration was genuinely concerned that the proposed bill would create “a serious erosion of credibility of the U.S. as a collective security partner in eyes of all allies, especially NATO.”

Closing the Commitment Gap After 1973

The sponsors of the WPR were keenly aware of the alliance commitment issue, and they had a specific solution in mind: standing force authorizations, today called authorizations for the use of military force (AUMFs). The Senate Report for the 1973 war powers bill, for example, specifically covered the topic of alliances and argued that “the bill envisages the adoption of treaty implementation legislation, as deemed appropriate and desirable by the Congress and the President.” Similarly, law professor Alexander Bickel, who was intimately involved in crafting the legislation, wrote: 

Our security and the peace of the world continue to depend in substantial measure on credible commitments undertaken by the United States and on a credible American capability to act in a crisis. … Far from eroding it, the [WPR] would substantially enhance it. Under the bill, the United States will be able to make credible international commitments through specific legislation implementing treaties and other agreements.

Javits, the primary sponsor of the legislation, was of similar mind, arguing, in a congressional hearing on the bill in early 1973, that a treaty like NATO would actually be strengthened by a strong WPR, because Congress would pass a standing authorization. Thus, influential architects of the WPR envisioned that a solution to the commitment gap further widened by the WPR was standing AUMFs. If this seems impractical, consider the political context. This was a moment at which, regardless of formal legal checks, a severely weakened presidency would have been especially constrained by public and congressional opinion. Therefore, compared to other moments in the modern presidency, the option of relying on presidential unilateralism to close the commitment gap seemed (to some reformists) impractical, too.

But no such authorizing resolutions were ever enacted after the passage of the WPR in 1973. Despite recognizing the issue, Congress’s reluctance to pass such standing authorizations is, perhaps, obvious: If the point of the WPR was to tighten congressional control over the use of force, passing standing resolutions would seemingly defeat that goal. If anything, the cure could be worse than the disease: When a president acted unilaterally, Congress could at least hold the absence of legislative approval over the executive’s head; a standing, bulletproof authorization, by contrast, would have effectively removed the stops on presidential action—or perhaps even emboldened the president to intervene in a bigger way than he would without express congressional backing. The executive branch didn’t push for standing legislative force authorizations, either, probably among other reasons because any divisive legislative debates would have made the commitment problem even worse. It is thus unsurprising that Congress never utilized the solution proposed by Bickel and Javits and envisioned by other WPR backers. Nevertheless, this left the now-widened commitment gap unresolved. 

This fact was not lost on U.S. allies, as several expressed their fear over the implications of the act. First and foremost, of course, was South Vietnam, but South Korea, Thailand, and the Philippines also expressed doubts about the U.S. alliance commitment post-1973. This meant that the executive branch needed to find another way to bridge the commitment gap: It had to restore an image of an imperial presidency in the eyes of allies and adversaries by demonstrating that it would not be burdened by the new WPR or other congressional restrictions. The Ford administration in 1975, for example, specifically averred an inherent presidential power to “carry out the terms of security commitments contained in treaties.” (An extensive 1993 Office of Legal Counsel opinion on the WPR also essentially endorsed the notion that the president may use force in defense of allies but raised questions about the outer bounds of that authority, especially if it involved prolonged, major war.) Talk is cheap, however, so ultimately the administration faced strategic pressures to prove the executive branch was not “hamstrung[.]” For example, in ordering a forceful response to the capture of the SS Mayaguez, Ford believed the American action demonstrated the president’s ability to act when needed: “We perhaps overreacted, to show the Koreans and other [allies] our resolve. … There were legislative restrictions imposed in the 1973 act and the War Powers Act, which some said meant the President couldn't act. This showed we could and did and showed the world we were’t hamstrung.” Hence, Ford’s decision to act decisively and overwhelmingly in the episode was undertaken, at least partially, with an eye toward reassuring American allies of the president’s ability to react swiftly in a crisis.

The WPR's history thus suggests that war powers and alliance commitments are entwined. While the drafters of the WPR clearly recognized that the credibility of extended deterrence and ally reassurance would be a problem under the act, Congress subsequently did not directly address the issue, which in turn put pressure back on presidents to act in ways that run contrary to the purposes of the WPR. Congress created a vacuum, and the president was forced to fill it once again.

Implications for War Powers Reform

In current debates mentioned above about how war powers and alliances intersect in important ways, there are essentially four main legal/policy orientations one might take: First, there are those who want to tighten legislative checks on war powers and who also want to pull back U.S. alliance responsibilities. For them, the tension between war powers checks and alliance commitment is not much of an issue. They often think the bigger problem is too much commitment, not too little. Second, there are presidential unilateralists who likewise want to weaken U.S. alliances, but for them presidential power is useful for American retrenchment rather than commitment. For them, the commitment gap is likewise solved by simply reducing commitments. Third, there are those who, by contrast, support strong U.S. alliance commitments but who tolerate presidential unilateralism. For them, the latter supports the former: An imperial presidency permits effective deterrence and reassurance. 

Finally, there are those who support tight legislative checks and strong alliances. This would include those who support WPR reform to make it more restrictive and enforceable and who also believe that the United States should maintain its global leadership role in sustaining alliances. For them, the question remains how to square the former with the latter. One might suppose that the appropriate path is for Congress to wait until crises or attacks occur and then pass specific force authorizations to deal with them case-by-case, but (for reasons that will be discussed in a future paper) we are skeptical that this approach will be sufficiently credible in adversaries’ and allies’ eyes. The point of U.S. alliances is to provide deterrence and stability, and it will be difficult for Congress to signal its commitment with requisite strength and clarity. Passing standing AUMFs would also seem to be a nonstarter for the historical reasons mentioned above, not to mention that doing so for some alliances but not others would entail its own problems.

Hence, those in the last camp need to squarely address the commitment gap in considering any potential war powers reform, and explain how they propose resolving it. No doubt, alliances today work differently than they did in the Cold War, especially as the United States works to rebalance defense burdens with many partners, but the United States remains the indispensable security guarantor in these relationships. Because alliances still require effective U.S. commitment, one of the solutions introduced above—or perhaps there are others—needs to be part of any effective war powers reform. Congress could legislate commitment; the president could continue to assert it; the president, perhaps with Congress, could tie the United States’ hands through things like placing troops in harm’s way; or the U.S. could loosen its alliance commitments and accept the foreign-policy consequences. Each of these solutions has its downsides. One way or another, though, robust alliance commitments will likely involve retaining in the president’s hands broad authority to act militarily in defense of allies.

Patrick Hulme is a Postdoctoral Research Fellow with the International Security Program at the Harvard Kennedy School's Belfer Center for Science and International Affairs, where he focuses on congressional-executive relations in U.S. foreign policy, deterrence theory, U.S.-China relations, and international security. He holds a J.D. from the UCLA School of Law and a Ph.D. in political science from UCSD.
Matthew Waxman is a law professor at Columbia Law School, where he chairs the National Security Law Program. He also previously co-chaired the Cybersecurity Center at Columbia University's Data Science Institute, and he is Adjunct Senior Fellow for Law and Foreign Policy at the Council on Foreign Relations. He previously served in senior policy positions at the State Department, Defense Department, and National Security Council. After graduating from Yale Law School, he clerked for Judge Joel M. Flaum of the U.S. Court of Appeals and Supreme Court Justice David H. Souter.

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