About the Authorization for Use of Military Force (AUMF)

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In the immediate aftermath of the September 11, 2001 attacks, the U.S. Congress passed a joint resolution that would fundamentally reshape American foreign policy and military engagement for a generation.

Contained within Public Law 107-40 is a single, 60-word sentence that serves as the primary domestic legal foundation for more than two decades of U.S. counterterrorism operations around the globe. This Authorization for Use of Military Force, or AUMF, granted the President the authority to use force against the perpetrators of the 9/11 attacks and those who harbored them.

What began as a specific mandate to pursue al-Qaeda and the Taliban in Afghanistan has since been interpreted by four successive presidential administrations to justify military actions in at least 22 countries, targeting a shifting array of groups, many of which did not exist on 9/11. This expansion has placed the 2001 AUMF, along with a separate 2002 authorization concerning Iraq, at the center of a profound constitutional debate over the separation of powers, the role of Congress in matters of war and peace, and the emergence of a state of perpetual, or “forever,” war.

This report explains what AUMFs are, traces the history and evolution of the post-9/11 authorizations, analyzes the controversies surrounding their use, and explores the ongoing debate over their potential reform.

War Powers in the Constitution

To understand the controversy surrounding modern AUMFs, one must first understand the constitutional framework the U.S. Founders designed for making decisions about war and peace. Wary of concentrating the power of the sword in the hands of a single person, as was common in the European monarchies they had fought to escape, the framers of the Constitution deliberately divided war powers between the legislative and executive branches.

The Founders’ Design

The Constitution creates what one scholar famously called an “invitation to struggle” between the President and Congress over the authority to commit the nation to armed conflict. The text grants Congress, the branch intended to be most accountable to the people, the most significant powers in this domain.

Article I, Section 8 explicitly gives Congress the authority to “declare War,” “raise and support Armies,” “provide and maintain a Navy,” and make rules for the military. James Madison, a key architect of the Constitution, articulated the logic behind this design, stating, “The constitution supposes, what the History of all Governments demonstrates, that the Executive is the branch of power most interested in war, and most prone to it. It has accordingly, with studied care, vested the question of war in the Legislature.”

The President, under Article II, Section 2, is designated the “Commander in Chief of the Army and Navy.” This role grants the President the authority to direct the military after Congress has authorized a conflict and, as confirmed by the Supreme Court in the 1863 Prize Cases, the inherent defensive power to “repel sudden attacks” against the United States without prior congressional approval.

The system was designed to ensure that the monumental decision to go to war could only be made with broad political consensus, requiring the cooperation of both branches.

Declarations of War vs. AUMFs

While the Constitution speaks of Congress’s power to “declare war,” this is not the only mechanism for authorizing military conflict. A formal declaration of war, last issued by the U.S. in 1942 during World War II, authorizes “total war.” This provides the President with the entire and unqualified use of the U.S. military and activates a wide range of standby domestic authorities related to the national economy and civil liberties.

An Authorization for Use of Military Force is a distinct legal tool. It is a statute passed by Congress that authorizes a more limited use of force for a specific purpose. Historically, AUMFs have contained constraints, such as clearly identifying the “named enemy,” defining the geographic scope of the conflict, setting a time limit or “sunset” provision for the authorization, or specifying the types of military “operations” that are permitted. This distinction is crucial for understanding the unique nature of the post-9/11 authorizations.

The War Powers Resolution of 1973

Throughout the 20th century, presidents increasingly committed U.S. troops to major conflicts like the Korean War and the Vietnam War without formal declarations of war, relying on their Commander in Chief powers and other justifications. In response to the perceived executive overreach during the Vietnam era, Congress passed the War Powers Resolution of 1973 over President Richard Nixon’s veto.

The law was intended to reassert Congress’s constitutional role. It requires the President to consult with Congress “in every possible instance” before introducing forces into hostilities and to submit a report to Congress within 48 hours of such a deployment. It starts a 60-day clock: if Congress does not explicitly authorize the military action or declare war within that period, the President is required to withdraw the forces.

While the War Powers Resolution remains law, its effectiveness has been a subject of continuous debate. Every president since 1973 has questioned its constitutionality, and administrations have often interpreted its requirements narrowly to avoid triggering the 60-day clock.

The 2001 AUMF itself represents a complex interaction with this law. While the AUMF’s text states it is intended to constitute the “specific statutory authorization” required by the War Powers Resolution, its broad and open-ended nature effectively provided a one-time, upfront approval for a conflict with no defined endpoint. This has allowed the executive branch to conduct counterterrorism operations for over two decades without ever needing to return to Congress for a new authorization, thereby circumventing the very mechanism of legislative review that the War Powers Resolution was designed to ensure.

The Post-9/11 Authorizations

In the wake of the September 11th attacks, Congress passed two distinct AUMFs that have since become the legal bedrock for America’s 21st-century wars. Though often discussed together, they were passed for different reasons, with different justifications, and have had vastly different legacies.

The 2001 AUMF

Passed just one week after the attacks, the 2001 AUMF was a direct response to a moment of profound national trauma and unity. The legislation, Senate Joint Resolution 23, moved through Congress with incredible speed, passing the Senate by a vote of 98-0 and the House of Representatives by a vote of 420-1. President George W. Bush signed it into law on September 18, 2001.

The core of the law authorizes the President:

“…to use all necessary and appropriate force against those nations, organizations, or persons he determines planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons, in order to prevent any future acts of international terrorism against the United States by such nations, organizations or persons.”

The original intent, as understood by Congress and the public at the time, was to grant the President the authority to pursue two specific entities: the al-Qaeda terrorist network that carried out the attacks, and the Taliban regime in Afghanistan that provided them with a safe harbor.

A critical piece of legislative history reveals that the final text was a compromise. The Bush administration had initially proposed even broader language that would have authorized force “to deter and pre-empt any future acts of terrorism or aggression against the United States.” Concerned that this would amount to a “blank check” for a global war on terrorism with no defined enemy, Congress pushed back and narrowed the language to specifically tie the authorization to the groups responsible for the 9/11 attacks. This deliberate limitation is central to the later controversy over the law’s expansive interpretation.

The 2002 AUMF

Passed in October 2002, more than a year after 9/11, the second major post-9/11 AUMF had a completely different purpose and justification. The Authorization for Use of Military Force Against Iraq Resolution of 2002 was not aimed at al-Qaeda but at the state of Iraq under the regime of Saddam Hussein. The debate leading to its passage was far more contentious, with the final vote being 296-133 in the House and 77-23 in the Senate.

The text of this law authorized the President to use the Armed Forces as necessary to “defend the national security of the United States against the continuing threat posed by Iraq; and enforce all relevant United Nations Security Council resolutions regarding Iraq.” The resolution’s preamble laid out a series of justifications, including Iraq’s alleged possession and development of chemical, biological, and nuclear weapons, its “brutal repression of its civilian population,” and its defiance of UN resolutions.

The fundamental difference between the two laws is the nature of the enemy they defined. The 2002 AUMF targeted a specific nation-state and its government. A conflict against a state has a natural, if often violent, endpoint: the defeat of its government and military. Once Saddam Hussein’s regime was overthrown in 2003, the primary mission of the 2002 AUMF was accomplished, rendering the law increasingly obsolete.

In contrast, the 2001 AUMF targeted fluid, non-state actors—”organizations or persons.” A conflict against a network or an ideology lacks a clear definition of victory or a singular point of surrender. This structural ambiguity is the core reason the 2001 AUMF became the legal architecture for an indefinite, expanding conflict, while the 2002 AUMF is now widely seen as a candidate for repeal.

How the War Expanded

The central controversy surrounding the post-9/11 AUMFs is how a law intended to authorize a specific response to the 9/11 attacks evolved into what critics call a “blank check” for a global, multi-generational war. This transformation occurred through a series of expansive legal interpretations by the executive branch, adopted and solidified on a bipartisan basis across four presidencies.

The “Associated Forces” Doctrine

The key legal innovation that enabled the expansion of the 2001 AUMF was the concept of “associated forces.” This term, which appears nowhere in the text of the 2001 law, was developed by executive branch lawyers to argue that the authorization to use force against al-Qaeda and the Taliban also applied to other terrorist groups that were deemed to be co-belligerents with them against the United States.

This interpretation was first asserted by the Bush administration, but it was legally formalized and defended in court by the Obama administration, particularly in the context of Guantánamo Bay habeas corpus litigation. This allowed the executive branch to use the 2001 AUMF to conduct military operations against groups like al-Qaeda in the Arabian Peninsula in Yemen and al-Shabaab in Somalia, even though these groups had little or no connection to the 9/11 attacks. The Trump and Biden administrations have continued to rely on this legal framework.

The Fight Against ISIS

The most significant and controversial application of this expansive legal theory came in 2014 with the rise of the Islamic State, or ISIS. ISIS did not exist on September 11, 2001. It originated as al-Qaeda in Iraq years later, and by 2014, its leader, Abu Bakr al-Baghdadi, had publicly broken with and been disavowed by al-Qaeda’s core leadership.

Despite this, the Obama administration argued that the 2001 AUMF provided the legal authority for a full-scale military campaign against ISIS in Iraq and Syria. The legal rationale was that ISIS could be considered a “successor” entity to AQI, which had once been formally affiliated with al-Qaeda. This created a tenuous historical link that the administration used to connect ISIS back to the original 9/11 authorization.

This interpretation was met with significant criticism from legal scholars and some members of Congress, who argued it stretched the 2001 law far beyond recognition and that a new, specific authorization for the war against ISIS should have been sought.

A Global Battlefield

The lack of any geographic limitation in the 2001 AUMF, combined with the “associated forces” doctrine, has transformed the “battlefield” into a global one. The AUMF has been cited as the domestic legal authority for U.S. military deployments and operations in a vast and growing list of countries, including Afghanistan, the Philippines, Georgia, Yemen, Djibouti, Kenya, Ethiopia, Eritrea, Iraq, Somalia, Libya, Syria, and Niger.

One report noted that between 2018 and 2020 alone, the U.S. initiated what it termed “counter-terror” activities in 85 countries, demonstrating the worldwide scope of the conflict being waged under this single, two-decade-old law.

Misuse of the 2002 AUMF

While the 2001 AUMF has been the primary vehicle for expansion, the obsolete 2002 Iraq AUMF has also been repurposed. The Obama and Trump administrations cited it as a secondary or “reinforcing” legal basis for the campaign against ISIS, arguing that because ISIS posed a threat to stability in Iraq, the 2002 law could apply.

The most controversial use came in January 2020, when the Trump administration claimed the 2002 AUMF provided legal authority for the drone strike in Iraq that killed Iranian General Qassem Soleimani. The administration argued that Soleimani posed a threat to U.S. forces in Iraq, thereby falling under the law’s purview. This assertion was widely condemned by legal experts and members of Congress, who argued that an authorization for war against Saddam Hussein’s regime could not plausibly be interpreted to permit strikes against officials of the government of Iran nearly two decades later.

This expansion of executive war-making power did not occur in a partisan vacuum. It has been a bipartisan, institutional process, creating a ratchet effect where the scope of presidential authority only grows. Each administration inherits the broader interpretations of its predecessor. By using those interpretations for its own military actions, it solidifies them as the new legal baseline.

Congress, for its part, has consistently appropriated funds for these expanding operations. The executive branch then points to this funding as implicit congressional “ratification” of its legal theories. This cycle—executive interpretation, followed by military action, followed by congressional funding interpreted as approval—makes the expansion of war powers incredibly durable and difficult to reverse.

The Human and Financial Cost

The legal and constitutional debate over AUMFs is not an abstract academic exercise. The broad interpretations of these laws have enabled a state of perpetual conflict with immense and tangible consequences.

According to analysis from the Costs of War Project at Brown University, the post-9/11 wars have cost U.S. taxpayers over $8 trillion. Another analysis calculated that taxpayers are paying $32 million every hour for the total costs of these wars. The human toll is even more staggering, with the same research estimating that over 900,000 people have been killed as a direct result of the post-9/11 conflicts.

The Push for Reform

In recent years, a broad, bipartisan consensus has emerged in Congress that the status quo of relying on two-decade-old war authorizations is unsustainable and constitutionally fraught. This has led to a multi-pronged effort to reform the AUMF landscape, focusing on repealing outdated laws and replacing the foundational 2001 AUMF with a more limited and accountable framework.

Repealing the 2002 AUMF

There is widespread agreement across the political spectrum that the 2002 AUMF, which authorized the war against Saddam Hussein, is obsolete and should be repealed. The Biden administration has formally endorsed its repeal, stating that the U.S. has no ongoing military activities that rely on it as a primary legal basis.

The primary arguments for repeal are straightforward:

It is no longer relevant: The Saddam Hussein regime was overthrown in 2003, and the U.S. combat mission in Iraq formally ended in 2011. The law that authorized a long-over war should be taken off the books.

It is not needed: The President retains inherent constitutional authority as Commander in Chief to defend U.S. forces and the nation against imminent attack, so repealing the 2002 AUMF would not affect defensive capabilities.

It is ripe for abuse: As demonstrated by its use to justify the Soleimani strike, leaving an outdated AUMF on the books creates a “loaded weapon” that a future administration could misuse to justify a new, unauthorized conflict.

Bipartisan legislation to repeal both the 2002 AUMF and an even older 1991 Gulf War AUMF, led by Senators Tim Kaine (D-VA) and Todd Young (R-IN) and Representatives Barbara Lee (D-CA) and Chip Roy (R-TX), has gained significant traction. Repeal bills have passed the House and the Senate in different congressional sessions, signaling a strong will to act, though the measures have not yet been reconciled and signed into law.

Replacing the 2001 AUMF

The more complex challenge is how to address the 2001 AUMF, which, unlike its 2002 counterpart, is still actively used as the legal basis for current counterterrorism operations. The consensus among reformers is that it should be repealed and replaced with a new, more carefully constructed authorization that restores Congress’s constitutional role.

Proposals for a new AUMF center on several key “guardrails”:

Sunset Clauses: Perhaps the most significant proposed reform is the inclusion of a “sunset” provision, which would cause the AUMF to automatically expire after a set period, such as two or three years. This would force Congress to periodically and publicly debate the status of a conflict and affirmatively vote to reauthorize it. Proponents argue this would prevent wars from continuing on “autopilot” for decades and restore democratic accountability.

Specificity Requirements: To prevent the “scope creep” that plagued the 2001 AUMF, reformers insist that any new authorization must be highly specific. This includes explicitly naming the terrorist organizations that are being targeted (a “named enemy” clause) and clearly defining the geographic regions where force is authorized (for example, specific “terrorist hotspots” like Iraq, Syria, and Afghanistan). This would prevent the executive branch from unilaterally adding new groups or countries to the target list.

Enhanced Oversight and Reporting: Reform proposals also include stricter and more transparent reporting requirements, compelling the executive branch to regularly provide Congress and the public with detailed information about where and against whom military force is being used under the authorization.

The Reform Debate

The push for AUMF reform is not without its critics and complexities. The debate boils down to a fundamental tension between the need for democratic accountability and the perceived need for executive flexibility in national security.

Arguments for Reform: Proponents, including a wide range of legal scholars, civil liberties organizations, and a bipartisan coalition of lawmakers, argue that reform is a constitutional necessity. They contend that Congress has abdicated its most solemn duty and that the current system allows one person, the President, to wage war around the globe with minimal oversight, leading to endless conflicts that are costly in both blood and treasure.

Arguments Against: Some policy analysts and officials express concern that overly rigid reforms could hamstring the U.S. response to dynamic and evolving terrorist threats. They argue that terrorist networks are not confined to specific countries and that new threats can emerge quickly. A sunset clause, they worry, could signal a lack of American resolve to adversaries and allies, while the hyper-partisanship of modern politics could prevent Congress from reauthorizing a necessary military operation in a timely manner, creating dangerous uncertainty.

The primary obstacle to meaningful reform may be less about legal theory and more about political incentives. For the executive branch, the current, broadly interpreted AUMFs provide maximum operational flexibility. For individual members of Congress, allowing the President to act under vague, pre-existing authority is often politically safer than taking a difficult, high-stakes vote to authorize a specific military action. This dynamic creates a powerful institutional inertia that favors the status quo, making the effort to restore the Founders’ vision of shared responsibility for war a profound and ongoing challenge.

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