AEA Litigation: Enforcing Congress’s Limits on Delegated Power

The Supreme Court’s Feb. 20 decision that struck down President Trump’s tariffs imposed under the International Emergency Economic Powers Act exposed fractured reasoning among the six-justice majority about the correct approach to statutory interpretation. If the Court had one overall message, however, it was that delegations of emergency power to the president should not be treated as invitations for the executive to grossly stretch statutory text to cover actions entirely unimaginable by the Congress that passed the law.

If this approach applies beyond the Trump administration’s tariff policy, Trump’s invocation of the Alien Enemies Act (AEA) nearly a year ago should also be declared illegal. The Trump administration’s use of the statute, aimed at alleged members of the Venezuelan criminal organization Tren de Aragua (TdA), has produced consequential litigation now pending before the U.S. Court of Appeals for the Fifth Circuit en banc, in W.M.M. v. Trump. The AEA is being used for the first time since World War II—and for the first time ever apart from declared wars.

The Supreme Court frequently directs that statutes be interpreted according to their meaning at the time of enactment. A legal-historical excavation of the AEA’s meaning in 1798, when it passed the Fifth Congress and was signed by President John Adams, is therefore required to answer the questions raised in W.M.M.

Because the AEA has been used only infrequently—just in the War of 1812, World War I, and World War II—no comprehensive scholarly analysis of the statute existed before Trump’s invocation in 2025.

I performed the historical research and compiled the findings in an academic article that examines the statute and its background, immediate context, and legislative purposes. Based on the article, I submitted an amicus brief in support of the detainees in W.M.M.

Here, I will describe the findings that lead me to conclude the statute is being used illegally today. Then I will note some hard questions raised in W.M.M. that are not resolved entirely by legal-historical analysis tied to 1798.

1798 Statutory Meaning

The AEA was enacted in July 1798 during the United States’s Quasi-War with France, a period of international crisis and domestic political polarization. The statute’s core provision remains largely unchanged today. In its modern codification, the AEA’s triggering language is as follows:

Whenever there is 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, and the President makes public proclamation of the event, all … citizens ... of the hostile nation or government ... who shall be within the United States and not actually naturalized, shall be liable to be apprehended, restrained, secured, and removed as alien enemies.

At first glance, that language may sound capacious. But to a lawyer or legislator in 1798, it was anything but. The Trump administration reads the AEA in a way that is contrary to how the text was understood in 1798.

The U.S. government asserts today that both “invasion” and “predatory incursion” in the AEA are terms that “include” but are “not limited to” “military attacks.” The briefing argues that the terms cover any “hostile entrance,” including “hostile acts of mass migration.” The government maintains that TdA actions in the United States fall within both of the statutory terms, because “TdA’s illegal entry and continued unlawful presence is an encroachment on U.S. territory that entails hostile acts contrary to the rights of citizens to be free from criminality and violence.”

The AEA’s most important term—“alien enemies”—was not one invented by Congress. In 1798, the term described a settled category in Anglo-American common law, the “law of nations” (a body of law that addressed international affairs, consisting of treaties, customary state practice, and natural law reasoning applied to states), and the practice of the British, American, and other governments. “Alien enemies” had a well-understood meaning: a subject or citizen of an enemy nation during a state of war. There was some nuance at the edges—such as what about a citizen of a neutral country who joins in a belligerent government’s prosecution of war? But a citizen of a wartime adversary nation was the core definition.

Alien enemy status arose categorically, based on nationality and the existence of war, not on individualized assessments of dangerousness, criminality, or intent. If Britain and France were at war, a French national in Britain was an alien enemy, whether or not he posed any threat. Conversely, outside of war, no one was an alien enemy. The law of nations and many U.S. treaties in force in 1798 reflected these legal understandings. In a post-World War II decision, the Supreme Court held that these definitions still prevailed about two centuries later.

At the time the AEA was enacted, both Congress and the executive branch understood and accepted that the Constitution had committed to Congress’s judgment (a) whether to initiate war; (b) the decision about how the United States should respond if war is initiated against the United States by formal declaration or military attack; (c) control over many forms of coercion against foreign persons or property that might be called “lesser” war powers, which were often measures that preceded or occurred with war, such as prize captures at sea, property confiscation on land, and embargoes; (d) and the decision whether to detain persons as alien enemies in war.

The AEA was drafted with this constitutional background in mind. The separation of powers came up frequently in Congress during the drafting process and is reflected in the AEA’s text. The AEA was also written to be consistent with protections for peaceful civilian alien enemies found in U.S. treaties and the law of nations. Ultimately, Congress decided to delegate power to the president to treat a foreign country’s nationals as alien enemies only when Congress or the foreign country had declared war, or when an actual military attack on U.S. territory by a foreign government (an “invasion” or “predatory incursion”) had occurred, or when one was imminent (“attempted” or “threatened”).

This last situation granted the executive branch a preemptive power over foreign nationals in cases of imminent war. The AEA passed because Federalists and some Republicans supported it. Compared to the Federalists, the Republicans tended to be more pro-French, concerned with the civil liberties of noncitizens, and skeptical of the John Adams administration’s motives and actions. If the AEA had dramatically expanded the traditional understanding of alien enemies, as the Trump administration contends, Republicans would likely have done everything they could to kill the bill.

We know this because, in 1798, Republicans were outraged by a Federalist bill that allowed the president to detain and deport noncitizens of any nationality outside of the context of war. This law, An Act Concerning Aliens (“Aliens Act”), was referred to by Republicans derisively as the Alien Friends Act, because it, in their view, violated the Constitution and international law by allowing harsh treatment of aliens from friendly, non-wartime enemy states.

It made sense to Congress in 1798 that the AEA would delegate power to treat foreign nationals of a hostile nation as alien enemies in a situation of imminent military attack on U.S. territory. At the time, news from abroad—for instance, a French fleet leaving port for a potential U.S. invasion, or Spain sending an army to land in its Florida territory to prepare a land-based attack—moved slowly across the Atlantic Ocean and along roads traveled by horse and carriage. Congress was often out of session, and it could not assemble rapidly. A “threatened” invasion or incursion would have been thought to exist when a foreign country’s fleets or armies had gathered off the U.S. coast or near a U.S. land border, preparing an attack. When war was imminent because of a looming attack on the U.S., Federalists, joined by some Republicans, saw no danger—constitutional, military, or diplomatic—and no violation of international law, from allowing the president to invoke a power to detain or remove the foreign countries’ nationals inside the United States as alien enemies.

My article, which seeks to pull together all available evidence of the AEA’s meaning in 1798, demonstrates that the question of statutory interpretation in W.M.M. has a clear answer. “Invasion” and “predatory incursion” refer to military attacks. The attacks must come from abroad—be “against the territory of the United States,” as the statute puts it. Simply put, no such attack has happened that would allow the AEA to be properly invoked by the Trump administration. Unwanted immigration, even when the immigrants are organized and commit crimes in the United States, does not qualify. People lawfully detained under the AEA must be properly considered “alien enemies” because they are nationals of a belligerent (wartime enemy) country. As noted, Congress codified this well-understood wartime category in 1798 rather than expanded it. No one in 1798 would have thought that TdA members could be properly considered alien enemies.

The Trump administration attempts to twist the AEA to turn it into a deportation statute for allegedly dangerous individual aliens. In the War of 1812, World War I, and World War II, presidents properly invoked the AEA categorically, designating all nationals of an enemy country present in the United States as alien enemies. Trump did not designate all Venezuelans as alien enemies, just alleged members of TdA. As noted, in 1798, Congress passed the Aliens Act that allowed the detention and deportation of dangerous noncitizens, irrespective of their nationality and of whether there was a state of war. The U.S. law today allows the same kind of protective actions. Because the Trump administration designated TdA as a Foreign Terrorist Organization and its members Specially Designated Global Terrorists (SDGT), provisions of the Immigration and Nationality Act allow dangerous individuals in these categories to be excluded from the country upon entrance, or detained for deportation if found in the United States. In both 1798 and today, ordinary criminal law is also designed to incapacitate dangerous individuals. The AEA is the wrong tool for the task the Trump administration is pursuing.

Some Additional Questions

There are at least three questions posed by W.M.M. that need further discussion because they might not be resolvable entirely by the 1798 statutory meaning. First, the consensus about the division of constitutional war powers that existed in 1798 has broken down. Since the 20th century—particularly since the undeclared Korean War—presidents have claimed substantial constitutional war powers to decide whether to initiate military attacks on foreign countries. Congress has largely acquiesced to these claims.

But that should not affect how the AEA is interpreted. Even today, presidents have very little, if any, independent constitutional power to detain foreign nationals present in the United States and cause their removal from the country. Congress clearly has substantial constitutional power over the topic, especially in war, but also in nonwar contexts. Congress’s powers come from a variety of places in the Constitution, including the Declare War, Captures, Foreign Commerce, and Necessary and Proper Clauses of Article I, and its “inherent” “sovereign” powers over immigration and deportation recognized by the Supreme Court since the latter part of the 19th century. Congress has the constitutional power to enact the AEA, and the president has little or no independent constitutional power on the topic. Thus, the president is bound to follow Congress’s statute as written. That’s the lesson of the Supreme Court’s famous decision in Youngstown Sheet & Tube Co. v. Sawyer (1952), as well as the recent tariffs decision, Learning Resources, Inc. v. Trump.

It should not matter that Congress wrote its specific delegation of power in the AEA based in part on an understanding of the constitutional division of war powers that has changed. Nothing in the intervening years of constitutional development transferred control over alien enemy detention and removal from Congress to the president. In 1798, the president had to follow Congress’s statute on alien enemies, and still does today.

A second issue concerns the relevance of events that occurred after the AEA was invoked in March 2025. Since then, the Trump administration first conducted lethal strikes on the high seas against alleged TdA vessels bringing drugs to the United States. The administration then informed Congress that the United States was in a “noninternational armed conflict” with TdA and several other gangs. These U.S. military strikes were followed by the U.S. imposing a partial naval blockade on Venezuela, aimed at interdicting petroleum exports.

And then, in early January 2026, U.S. air and land attacks captured Venezuelan President Nicolás Maduro. The Department of Justice’s Office of Legal Counsel provided an opinion blessing the legality of this, justified as a use of “military personnel to assist law enforcement in forcibly removing Maduro from Venezuela to the United States for prosecution.”

These recent events raise several questions—though, for some reason, the judges of the Fifth Circuit (sitting for rehearing en banc) did not ask them at the recent oral argument. Does the “Maduro regime,” a foundation of Trump’s invocation of the AEA because it ties TdA to a “foreign nation or government” in the AEA’s first section, still exist, and if not, does that matter? On this question, the habeas petitioners and the government have taken different positions before the court. Although the Supreme Court has held that the president has an exclusive constitutional power to decide whether and how to recognize the legal existence of foreign governments, one would think that Maduro’s ouster, and his pretrial custody in a federal detention facility in New York City, should make it rather difficult to conclude that he still runs the Venezuelan government and still (allegedly) partners with TdA. A court ruling for the detainees need not resolve this question, however. It could assume, for the sake of argument, the continued existence of a Venezuelan government-TdA connection but hold that the proclamation does not satisfy the AEA in other respects.

Another potential question raised by these events is the legal impact, if any, on the W.M.M. litigation of the episodes of armed conflict between the United States and Venezuela that occurred after the AEA proclamation. They should be irrelevant, because the AEA is not triggered by armed conflict but by much more specific terms—“declared war,” or attempted, threatened, or perpetrated “invasion” or “predatory incursion” “against the territory of the United States.” No new events have occurred since March 2025 that could be said to be an invasion or predatory incursion against the territory of the United States as those terms were understood in 1798. The AEA proclamation must stand or fall based on its assertions about TdA illegally emigrating to and then operating in the United States.

A third issue raised by W.M.M. concerns the amount of deference courts owe to the president’s proclaimed findings that an “invasion” or “predatory incursion” under the AEA has in fact occurred. Many of the Fifth Circuit’s questions at oral argument focused on this topic

The Supreme Court has had three important AEA cases on the scope of judicial review and deference to the executive: a 1948 decision and two decisions on its 2025 interim orders docket. In those cases, the Court held that persons detained under the AEA have a constitutional right of notice and a reasonable opportunity to be heard in a habeas proceeding by a court prior to removal, and that the Constitution further requires that alleged alien enemies may raise in these habeas proceedings (a) whether the notice and opportunity to be heard were consistent with the Due Process Clause; (b) “whether the person restrained is in fact an alien enemy” under the terms of the act; (c) and questions of the “interpretation and constitutionality” of the act, also described by the Court as questions of “the construction and validity of the statute.” Somewhat confusingly, the Court also states that the AEA “largely ‘preclude[s] judicial review[.]’”

More understandable is the Supreme Court’s caution that “[t]he very nature of the President’s power to order the removal of all enemy aliens rejects the notion that courts may pass judgment upon the exercise of his discretion”—speaking about decisions to deploy the “very great discretionary powers respecting the[ ] persons” of alien enemies conferred by the AEA. This discussion comes from the part of the Court’s 1948 decision in a World War II-era case about who decides whether a given German alien enemy is dangerous and should be detained or removed. The president is given unreviewable discretion on this question, the Court held.

In its few decisions, the Supreme Court has not fully specified how far judicial review under the AEA may extend, and what kinds of executive-branch decisions, in addition to discretionary ones about whom precisely to detain and remove, may be committed entirely to the president’s determination. The 18th-century materials I review in my article do not speak definitively about these questions.

But there is a plausible way to resolve W.M.M. that sticks close to what the Supreme Court has said clearly, and avoids most of the potentially difficult questions about deference and reviewability. Statutory interpretation has been expressly described by the Supreme Court in AEA cases as a judicial function, and the Trump administration’s construction of the statute is clearly incorrect. When the U.S. government asserted at oral argument that the president alone may decide how presidentially determined facts apply to the judicially determined law of the AEA, one of the judges interjected, “[w]hy are we construing [the AEA]” then? “Just for the fun of it?” The government wants the president’s assertion that there has been an invasion and predatory incursion to be treated as conclusive. The Fifth Circuit judge’s point was that there must be some judicial role besides just a sterile declaration of what the law is. The judge could have added that, as noted above, the Supreme Court has held that “whether the person restrained is in fact an alien enemy” under the AEA is judicially reviewable.

If the court correctly determines that “invasion” and “predatory incursion” refer to military attacks launched against U.S. territory, it could rule for the habeas petitioners without needing to resolve all possible questions about deference to the president. The court could decide to take at face value all specific factual assertions in Trump’s proclamation but hold that they do not allege any military attack on U.S. territory by a foreign nation or government.

The proclamation asserts in a conclusory fashion that TdA is “undertaking hostile actions and conducting irregular warfare against the territory of the United States” and “is perpetrating an invasion of and predatory incursion into the United States.” These general assertions simply mimic the statutory language, with some extra color added. If conclusory recitation of statutory triggering words must be treated as binding on the courts, then the president can invoke the AEA whenever he wants, and much of allowable judicial review under the AEA described by the Supreme Court would seem to be rendered meaningless.

The World War II-era decision, Ludecke v. Watkins (1948), held that the courts in that AEA case could not look behind the political branch’s decision to leave the state of war created by Congress’s 1941 declaration of war against Germany in place, even though the actual warfighting had ended:

War does not cease with a cease-fire order … [The] state of war [created by Congress’s declaration] may be terminated by treaty or legislation or Presidential proclamation. Whatever the modes, its termination is a political act.

Today, Congress has not declared war against Venezuela, and so the AEA must be triggered, if at all, on other grounds—“invasion” or “predatory incursion.” There is somewhat less clarity in these circumstances about the political versus judicial role under the AEA in determining whether the statute was properly invoked.

Pulling together the Supreme Court’s guidance, it seems most appropriate for the court in W.M.M. to examine the Trump proclamation’s specific factual assertions to determine whether they meet the statute’s triggering requirements, rather than simply deeming conclusive the proclamation’s more broad pronouncements that the statute is properly invoked. Treating the specific factual assertions as true and asking whether they describe events that meet the AEA’s triggers does not seem to invade the type of presidential “discretion” the Supreme Court has discussed.

When one turns to the Trump proclamation’s specifications of TdA’s actual conduct, the text does not describe a military attack against U.S. territory. The proclamation states that TdA has “unlawfully infiltrated the United States” through “mass illegal migration”—describing entry in violation of immigration laws, not military attack. The proclamation continues that TdA “commits brutal crimes, including murders, kidnappings, extortions, and human, drug, and weapons trafficking.” These are not military attacks. The SDGT designation, covering TdA and a variety of other drug cartels, does not describe any actual or imminently threatened military attack against the territory of the United States by TdA.

Similarly, to the extent it might be relevant, the superseding indictment of Maduro filed by the U.S. Attorney’s Office in Manhattan describes Maduro as having “partnered with narco-terrorists,” including TdA. The indictment continues that TdA is a “violent transnational criminal organization” whose members engage in crimes including “human smuggling,” “drug trafficking, firearms trafficking,” “theft, fraud, extortion,” and “murder ... to enforce and further the organization’s criminal activities.” Again, this is not a description of a military attack against the territory of the United States by a foreign nation.

If mere presidential say-so that an attempted, threatened, or actual “invasion” and “predatory incursion” has occurred were to be deemed fully sufficient by the courts, the AEA would amount to a blank check that the executive branch could use in ways Congress never intended. Detainees would get only the form but little of the substance of the judicial review they have been promised by the Supreme Court. In W.M.M., the court can—and should—rule that the AEA is being applied illegally without needing to decide all of the potential questions about judicial deference to the president under the AEA.