The Alien Enemies Act of 1798 (AEA) is a wartime authority. Congress enacted the AEA under its constitutional war powers as an implementation of the law of war, which in 1798 allowed the government to detain or expel supposed “alien enemies.” The AEA may be invoked only in the event of a declared war, “invasion,” or “predatory incursion” by a foreign nation or government against U.S. territory. It has no peacetime applicability and has never been used outside of a major conflict. Before now, the only time the AEA was invoked absent a declared war was after Japan’s attack on Pearl Harbor on December 7, 1941, just days before Congress declared war.

The Trump Administration’s current invocation of the AEA, “Invocation of the Alien Enemies Act Regarding the Invasion of the United States by Tren de Aragua,” falls well outside the law’s scope. By its text, the Proclamation addresses unlawful migration, narcotics trafficking, and gang violence, none of which constitute an “invasion” or “predatory incursion.” Under no interpretation of the law of war could these civil and criminal matters trigger the AEA’s exceptional powers. The designation of the Venezuelan drug gang Tren de Aragua as a foreign terrorist organization (FTO) does not transform its activities into acts of war.

A group of people at risk of imminent removal under the Proclamation filed a lawsuit in Texas on their own behalf and on behalf of others similarly at risk. They asked a federal district court to temporarily block the government from removing anyone under the Proclamation. The federal court denied that request, believing that there was not a sufficient risk of imminent removal. Now the plaintiffs have asked the Fifth Circuit Court of Appeals to block the government from removing anyone pursuant to the Proclamation. And Cato has joined the Brennan Center and Professors Ilya Somin and John Dehn to file an amicus brief supporting that request.

In our brief, we explain that this case does not present a political question exempted from judicial review. But even if it did, established exceptions to that doctrine would apply. Courts may always check obvious mistakes and manifestly unauthorized exercises of power. And the judiciary’s ability to act is at its apex when civil liberties are at stake. Courts have the power to correct the president’s misappropriation of the AEA in peacetime, and courts can rely on the judicially manageable standards historically used to identify acts of war.

Should courts adopt the government’s unfounded interpretation of the AEA or hold that the executive’s pronouncements are unreviewable, there would be dire consequences. The president could leverage the law’s power against any group of immigrants, including legal ones. The federal government could suspend the writ of habeas corpus at will, and states could “engage in War” at any time. The Fifth Circuit should block the Proclamation from going into effect.