What are “Wartime Authorities” and When Can the President Use Them? An Expert Q&A

The first several months of President Donald Trump’s second administration have been marred by the chaotic and often unlawful use, or threatened use, of wartime and terrorism-related authorities for what are essentially domestic immigration or criminal law enforcement purposes. This is not the first time a president has sought to push the boundaries of his wartime powers, or outright claimed those he did not have, but it may well be the most extreme. Indeed, Trump’s reliance on wartime authorities in contexts entirely divorced from armed conflict, or even the threat of force against the United States, puts the country on a novel and highly dangerous path. This is especially so given the extent to which he and his administration are demonizing and dehumanizing the people against whom they have aimed such powers. The language Trump is using has both political and legal aims; by using the rhetoric of war he seeks to legitimize his aggrandizement of power and his persecution of vulnerable populations.

While the Constitution grants most war-making and regulating power to Congress, the courts and Congress together have, over the decades, ceded significant authority to the executive branch. As a result, the presidency today exercises extraordinary powers and discretion during war. That concession, however, comes with the understanding that these authorities apply in limited, and exceptional, contexts. It is essential, therefore, to understand the line between war and peace, carefully scrutinize any attempt to apply wartime powers to novel circumstances, and interrogate the president’s assertions when he claims power to trigger them.

There has been a good deal written on these pages about many of the authorities that we address below. Our goal with this explainer is to unpack them in one place for policymakers, judges, journalists, practitioners, and others seeking to navigate these concepts. We seek to foster understanding of what these authorities are (and aren’t) intended for, what they do (and don’t do) in practice, how (if at all) they are related, and why it is crucial to maintain a bright line between when wartime authorities apply and when they do not.

In the hope of making what follows easily accessible and digestible, we answer the following questions (for ease of reference, click on any to jump to the relevant section):

When is the United States “at war”?

What are “wartime authorities”?

When has the United States used wartime authorities before?

What is the Alien Enemies Act and what can it be used for?

What is a Foreign Terrorist Organization (FTO) and what does such a designation do, and not do, in practice?

Can the president use force to attack drug traffickers or other criminal enterprises?

What is an Authorization for Use of Military Force (AUMF)?

What is the 2001 AUMF and what can it be used for?

What about the other authorities President Trump is invoking at the border and for immigration enforcement?

Q. When is the United States “at war”?

A. Whether a country is at war is a question of fact. States have developed fact-based tests for determining whether a state is engaged in an “armed conflict,” which is the terminology used under modern international law. The specifics differ somewhat based on the type of parties involved (whether the armed conflict is among states, or involves a state fighting a non-state actor; and so on). The term “armed conflict” is applied particularly carefully when non-state actors are involved, requiring a certain level of intensity and duration of fighting, and that the non-state actor be a sufficiently organized armed group (as opposed to a collection of criminal actors or loose grouping of individuals that share an ideology).

But in all cases it is the facts on the ground that matter, not anyone’s rhetoric. In fact, it is precisely because states knew all too well that political calculations might affect how leaders choose to characterize facts on the ground that they enshrined this recognition explicitly in the Geneva Conventions.

As one of us (Tess) has explained previously, “[a] state of armed conflict makes lawful a range of actions that would be illegal outside of war and springs to life whole bodies of law not applicable in peacetime.” It triggers both domestic U.S. statutes and a specific body of international law (the set of rules that governs the conduct of hostilities within armed conflict, and is often referred to as the law of armed conflict (LOAC), international humanitarian law (IHL), the law governing the conduct of hostilities, or the laws of war, which derive from a combination of treaties such as the Geneva and Hague Conventions as well as customary international law, and which the United States has long been heavily engaged in promulgating and promoting).

Detention and lethal targeting based on status alone can be lawful during war, as can prosecution before military tribunals. But “[t]he resort to these extraordinary authorities, and the ease with which the President may do so in war, are intended to be exceptions to normal order.”

Q. What are “wartime authorities”?

A. The phrase “wartime authorities” is not a legal term of art per se, but is often used to refer to the powers given to Congress and to the president, respectively, under the U.S. Constitution during times of war, as well as a host of statutes passed by Congress that are applicable in wartime. Many of those statutes in turn grant the president far greater powers than the sparse authority the Constitution alone allocates in Article II.

First and foremost, the Constitution provides Congress with a range of authorities that it may exercise on behalf of the United States during war, as well as to prepare for or prevent war. These include the power to declare war, to police the edges of when the country goes to war (which it used to seriously constrain the executive branch in earlier wars in U.S.history), to raise and support armies, to provide and maintain a navy, to provide for the common defense, to regulate detention and seizure of vessels in war, to regulate the military, to decide how offenses against the laws of war (war crimes) are punished, among several others.

The president is granted limited wartime authority in the Constitution, most notably as “Commander-in-Chief.” This position is essentially an operational role as commander of the armed forces during war, but one that has taken on expanded meaning (and been the subject of major interbranch controversy) in recent practice. Most agree the framers intended the president to retain some unilateral power to “repel attacks,” but in recent decades successive presidential administrations have used force in ways that are completely untethered from an attack on the United States or even a threat thereof. Presidents have justified these claims under a theory that the president may use force as long as it does not rise to the level of “war in the constitutional sense” (judged in theory based on the DOJ Office of Legal Counsel’s assessment of the nature, scope, and duration of the force to be used), at which point, under that view, it would implicate the power the Constitution granted Congress.

This brief overview of the Constitutional division of wartime authorities between Congress and the executive branch may seem lopsided toward Congress – that’s because it is, or at least was intended to be. The framers divided wartime authorities this way on purpose: putting the authority to decide when and why the nation goes to war in the hands of the slower, more deliberative body, and the one closer to the people, was a feature, not a bug.

Relying on the wartime authorities provided in Article I of the Constitution, Congress has passed a wide range of statutes applicable in armed conflict, or to police the boundaries of it. Many of these grant authority to the president to take specified actions during wartime. These are things like applying extraordinary economic sanctions, or using force against specified groups, such as those responsible for the 9/11 attacks. Others, like the landmark War Powers Resolution of 1973, are intended to put constraints on the president’s ability to wage war without congressional approval and reset the Constitutional balance that gave Congress, not the president, the decision when to go to war.

The courts, for their part, have in recent decades ratified significant power for the president to act unilaterally in wartime, for example to detain without charge even American citizens captured in a Congressionally authorized armed conflict, for its duration. In other cases, the courts have reined in the president’s overreach, even in war.

On balance, the courts and Congress together have granted the president extraordinary wartime authorities. But they have done so with the understanding that these powers apply in limited, and extraordinary, contexts. The only way to rein in these powers – or even just limit them to the already aggrandized status quo – is for Congress, and when possible the courts, to play their assigned roles in checking the president when he steps over the line.

Q. When has the United States used wartime authorities before?

A. American Presidents have relied on wartime authorities during a range of actual armed conflicts, from the pre-Civil War era to World War II, among many others. Some uses of wartime authorities have been more controversial than others in terms of, for example, their unilateral invocation, the degree to which interpretations of the scope of authority are broadened, and whether they are implemented in a way that is consistent with the United States’ international obligations.

Today, Trump is asserting authority to use wartime authorities outside of war to grab unilateral (and, so he claims, often unreviewable) power in areas ranging from detention and removal of immigrants (including repeated circumstances where they face grave harm), to potential targeted killing of criminal actors abroad, to tariffs on foreign nations.

In some of these areas, Trump appears to be emulating the playbook used by the George W. Bush administration in the aftermath of the 9/11 attacks. He is being assisted by the United States’ failure to grapple sufficiently with many post-9/11 abuses – but he is applying this playbook in a radically different context.

Facing the first armed attack on U.S. soil since Pearl Harbor in 1941, the Bush administration built a legal and policy architecture that sought to authorize the widespread use of lethal force abroad; indefinite detention without charge or meaningful review; extraordinary rendition (kidnapping or capturing people and sending them to countries where they face a high risk of torture or abuse in interrogations); and torture itself. It approached a large swath of domestic issues, some aspects of immigration included, through a counterterrorism or security lens: it racialized and targeted Muslim men, and more generally sowed fear among communities of color.

The courts and Congress pushed back on many of the more extreme claims of power – in particular on inhumane treatment of detainees and attempts to create legal black holes to detain them entirely beyond the reach of courts. So too did international institutions and some U.S. partners abroad who had joined the United States in fighting al Qaeda. Even the Bush administration itself began winding down parts of its sprawling “Global War on Terror” as it became clear how counterproductive it was to long-term U.S. interests. Nevertheless, U.S. courts and Congress (as well as many international partners and institutions) accepted and entrenched the overall framework of applying wartime authorities to this then-novel transnational conflict with a non-state actor, at least in the context of a congressionally authorized armed conflict.

Q. What is the Alien Enemies Act and what can it be used for?

A. The Alien Enemies Act is a centuries-old statute that has only been invoked a few times in U.S. history, most recently during World War II. As one of us (Bec) recently explained:

On March 15, 2025, President Donald Trump issued a proclamation titled, “Invocation of the Alien Enemies Act Regarding the Invasion of The United States by Tren De Aragua.” In purporting to invoke the Alien Enemies Act, Trump resurrected a 1798 statute that grants the President extraordinary removal powers in times of “declared war” or “invasion or predatory incursion … against the territory of the United States by any foreign nation or government.” Specifically, this wartime power permits the President to apprehend and remove as “alien enemies” the non-U.S. citizen nationals of the foreign state, as long as they are fourteen or older. Removal is not based on danger, or evidence of a crime, or immigration status. The act thus places significant discretion in the hands of the President in times of war.

This power granted by Congress turns entirely on the predicate questions: whether there is a “a declared war between the United States and any foreign nation or government, or any invasion or predatory incursion is perpetrated, attempted, or threatened against the territory of the United States by any foreign nation or government.”

Prior to this year, the AEA had been invoked a grand total of three times, all during congressionally declared wars between nation-state militaries (the War of 1812, World War I, and World War II). It has never been used outside of such contexts, much less as a stand-in for basic immigration enforcement.

Q. What is a Foreign Terrorist Organization (FTO) and what does such designation do, and not do, in practice?

A. The Trump administration has designated several drug trafficking organizations as FTOs. As Brian Finucane writes, this is part of an effort “to cast drug trafficking organizations as terrorists and hint at possibly using the tools of counter-terrorism direct action.”

“Foreign Terrorist Organization” is a designation made by the U.S. State Department under a statute created by Congress (Section 219 of the INA). The statute authorizes the secretary of state to designate an entity if the secretary finds the following:

(1) it is a foreign organization;

(2) it engages in “terrorist activity,” “terrorism” as broadly defined in statute, or retains the capability and intent to engage in terrorist activity or terrorism; and

(3) it threatens the security of U.S. nationals or the national defense, foreign relations, or economic interests of the United States.

The definition of “terrorist activity” includes engaging in specified acts of violence as well as soliciting funds for a designated organization, providing material support (including safe houses, funds, transport), or using an explosive or weapon with intent to cause damage to persons or property.

FTO designations carry significant and far-reaching consequences, sometimes including for people who have little or nothing to do with the entity itself. And there are significant issues inherent in the conflation between ordinary criminal activity and terrorism, as others have discussed. There is also a risk the language of “terrorism” may cause confusion over the consequences of such a designation, which may be by design in the current administration.

To be clear, an FTO designation does not require or create a “war” or “armed conflict” between the designee and the United States (or any state). It does not trigger any of the “wartime authorities” discussed above or below.

Most pertinently given recent reporting, an FTO designation does not authorize detention or targeting of members of the organization, as will be discussed further in the next question. And, contra one judge’s reasoning in an AEA case, it does not trigger the application of statutes that use terms like war or armed conflict or “invasion.”

Q. Can the president use force to attack drug traffickers or other criminal enterprises?

A. There have been reports that the administration is considering strikes on criminal organizations or their leaders abroad, such as drug cartels in Mexico.

Any use of force by the president against entities or states that have not themselves engaged in an armed attack against the United States (or a credible and imminent threat thereof) would violate international law, as enshrined in the U.N. Charter, in addition to the Constitutional separation of powers, which gives that decision to Congress. (An exception would be if another country asked the United States to use force based on a legitimate claim of collective self-defense, but that too would require congressional authorization as a domestic law matter.) That fact remains notwithstanding the Trump administration’s claims, and threats, to use any of the above-described statutorily granted authorities, and regardless of the rhetoric he may deploy in claiming such authorities. As discussed above, an FTO designation does not make an entity, or an individual connected to such an entity, a lawful target of force.

Moreover, when the United States uses force, any individual strike must also comport with the law of armed conflict, which regulates what states (and other parties to conflict) may do within armed conflict. These rules require parties to a conflict to distinguish between combatants and civilians in their targeting. The principle of distinction, among the most critical rules governing states at war, holds that the civilian population must be protected and cannot be made the direct subject of attack. Combatants, under the laws of war, are not criminals simply by their lawful participation in the conflict. And mere criminals are not combatants; they are civilians who retain their protections as such (unless and only for such time as they participate directly in hostilities in an actual armed conflict).

Putting aside the likely disastrous human and political consequences of starting a war with a neighboring state, a use of force against a mere criminal enterprise, such as a drug cartel that does not constitute an organized armed group engaged in an armed conflict, would thus be illegal on numerous grounds:

1) It would involve an unlawful use of force against an entity, and within a state, that has not attacked the United States. It would thus likely constitute an armed attack on that state itself, which could create a self-defense justification for that state to respond with force against the United States.

2) If the president were to use force absent congressional authorization specifically enacted for these purposes, such an act would violate the Constitutional separation of powers.

3) And finally, any attack on a drug cartel as such would entail a targeted killing of civilians: this in itself is a war crime.

Q. What is an Authorization for Use of Military Force (AUMF)?

A. The Constitution gives Congress the power to declare war, and Congress has long fulfilled that role not only in formal declarations of war but also in authorizations to use military force.

In fact, Congress has not formally declared war since World War II. This avoidance converged with the world’s burgeoning efforts to ban war as a lawful means of resolving disputes, ultimately codified as the prohibition on the use of force in Art. 2(4) of the UN Charter. The terminology of the “declare war” clause is thus rooted in a bygone era when war was a lawful tool of policy available to states. In the modern era, the use of force is permitted only under narrow circumstances and must be justified by self-defense or a UN Security Council Resolution.

So too the language of war has changed. We speak instead of states “using force” in response to an “armed attack,” and “armed conflict” for states involved in ongoing hostilities between their militaries. As noted above, the term “armed conflict” may also apply to a conflict between a state and a non-state actor, if the latter is an organized armed group involved in prolonged hostilities that have reached a certain level of intensity.

Thus, while Congress has not “declared war” in the modern era, it has nevertheless regularly fulfilled that same constitutional function by authorizing the president to use military force in statutes, which we informally refer to as AUMFs.

Importantly, an AUMF may be limited in scope–it need not delegate to the president the full authority that Congress retains in deciding how and when the nation uses its military power. Congress may, for example, limit the actors against which force may be used, the locations where force may be used, the duration of a deployment or engagement, or even specify certain types of military activity that are prohibited (i.e., it may limit the use of ground troops).

Q. What is the 2001 AUMF and what can it be used for?

A. The most notorious such statute at this moment is the 2001 AUMF, which Congress enacted in the aftermath of 9/11 to authorize the president to use force against the entities responsible for 9/11, namely al Qaeda and the Taliban (which was then, as it is now, the government of Afghanistan).

Congress quite intentionally did not accept at that time the broader delegation of power that the George W. Bush administration had requested, essentially to use force to fight all terrorism. Instead, the AUMF it passed was limited in the actors against which it permitted the use of force, and it specified the purposes for which force could be used (specifically, force could be used “in order to prevent any future acts of international terrorism against the United States by such nations, organizations or persons”).

Nevertheless, in the 24 years since Congress passed the 2001 AUMF, presidents have used it to justify the use of force against not only the groups originally referenced, but also groups that have, in the U.S. government’s terms, “joined the fight” between al Qaeda or the Taliban and the United States, under a purported theory of “co-belligerency.” One of us (Bec) has explained why the concept of co-belligerency cannot be a source of domestic authority for the president to act unilaterally. In 2014, an even more controversial expansion purported to extend the AUMF’s coverage to ISIS, an armed group that was then in open conflict with al-Qaeda, but was viewed as the “successor” to groups that had previously been determined to fall within the AUMF’s scope.

The government’s theory with respect to “associated forces” has been ratified in some limited contexts–with groups that have links to al Qaeda–by courts and even Congress. The most sympathetic read of that argument is one of congressional intent – the idea being that Congress intended to encompass any group that “joins the fight” alongside al Qaeda when it passed the law. The question remains then how narrowly we should construe a limiting principle.

Even accepting the broadest possible construction, there is absolutely no plausible argument to tie either the 2001 AUMF or the 2002 AUMF (authorizing war in Iraq) to an immigration context or criminal enterprises like narcotics producers.

Q. What about the other authorities President Trump is invoking at the border and for immigration enforcement?

A. There are a host of other authorities that the president has invoked to aggrandize his power on the basis of a claimed emergency or other exceptional basis – in contexts including but not limited to immigration and law enforcement – that are not wartime authorities per se but that generally rely on national security-related rationales. These include, among others, the Insurrection Act, the National Emergencies Act of 1976, and the International Emergency Economic Powers Act (IEEPA). Several of these are addressed here in a Just Security article by Bill Banks.

In brief: The Insurrection Act is a combination of statutes passed in the 18th and 19th centuries that permit the president to deploy the military domestically – a suspension of the Posse Comitatus Act – to address “rebellion against the authority of the United States” or other events that “make it impracticable to enforce the laws of the United States in any State by the ordinary course of judicial proceedings.” At the time of this writing, the Insurrection Act has not been invoked, but a Trump executive order and other rhetoric have suggested he may seek to use it despite the lack of factual predicate for doing so, in particular “to obtain complete operational control of the southern border….” This would be an entirely novel use of the act to address circumstances that are clearly not contemplated by the statute.

The National Emergencies Act (NEA), passed by Congress in 1976, imposes guardrails on the president’s exercise of emergency powers. It is not a “wartime authority” per se, and is most often used in non-conflict related contexts. Nor does the NEA create any new powers in and of itself. The law requires that national emergencies be formally declared by the president, though the statute does not define that term nor does it set out substantive criteria for doing so. The law also requires the president to specify the statutory authorities being invoked (which are contained in more than 130 laws). Unless renewed, states of emergency expire after one year. Congress can terminate a national emergency sooner (or anytime) via joint resolution and through a fast-track procedural process, but it must be signed by the president or, more realistically, supermajorities in both chambers must override a presidential veto, for it to become law. In practice, national emergencies, once declared, are often renewed indefinitely.

The NEA is most commonly used – indeed, in all but five of the emergencies declared since its enactment – to invoke IEEPA’s powers such as freezing assets and imposing sanctions. (As of this writing, Trump’s use of IEEPA to impose a sweeping set of tariffs is the subject of active litigation). On his first day in office, Trump invoked the NEA to elicit certain types of military support in his effort to effectively close the southern border.

It is not at all outside the bounds for Congress and the courts to push back on such power grabs. In fact, one of the most significant Supreme Court cases on presidential power involved presidential overreach relying on statutorily delegated power in an actual wartime context. In the 1952 Steel Seizure case, the Supreme Court held that the president could not seize the nation’s steel mills to keep them operating despite a worker strike in the midst of the Korean War, in which U.S. forces were actively engaged abroad. Courts also checked presidential overreach during actual conflicts dating back to the “quasi-wars” of the late 18th century, and as recently as the early stages of the so-called “War on Terror” when the president claimed authority beyond what the Constitution, the Congress, and the laws of war allow. For its part, Congress has constrained presidential power even in the immediate aftermath of the 9/11 attacks, when it refused to grant the President total power to use force without defined limits, and later to protect detainees from abuse.

* * *

Many of us have long warned about the perils of ceding too much discretionary power to the executive branch. But in recent years the courts and Congress have been reluctant to interrogate the president’s assertions when he has claimed national security reasons or special intelligence insights for broad and novel uses of constitutional or statutory authority. Today, Trump seeks to capitalize on that reluctance. He invokes war, emergency, terrorism, and national security to claim extraordinary powers in the most ordinary of circumstances. The co-equal branches of government have a duty to ensure that today’s manufactured crises do not become a Trojan horse for the tyrannical exercise of executive power.