Trump is promising deportations under the Alien Enemies Act of 1798. What is it?

Former President Donald Trump, whose bid for the White House has been dominated by his increasingly hardline anti-immigration rhetoric, is vowing to use an obscure, centuries-old law to expedite the removal of undocumented migrants from the U.S.

“I will invoke the Alien Enemies Act of 1798 to target and dismantle every migrant criminal network operating on American soil,” he said at a recent rally in California, one of several in which he has brought it up.

Trump is promising that, if reelected, he will use the act to initiate a federal effort called “Operation Aurora” — named after the Colorado town that he claims has been taken over by Venezuelan gangs, which residents and local officials dispute — to target undocumented migrant gang members for arrest and deportation.

He has also suggested that the act could be used to end sanctuary cities, which limit cooperation with federal immigration authorities, telling Fox News’ Harris Faulkner that “we can do things in terms of moving people out.”

The Alien Enemies Act is featured in more than just Trump’s stump speech.

It’s also name-checked in the Republican Party’s official 2024 platform, which says it will invoke the law to “remove all known or suspected gang members, drug dealers, or cartel members from the United States, ending the scourge of Illegal Alien gang violence once and for all.”

The act has gotten relatively little attention, let alone use, in the more than 200 years it’s been on the books, as Trump acknowledged.

“Those were the old days, when they had tough politicians,” he told a crowd of supporters in Arizona. “Think of that, 1798. Oh, it’s a powerful act. You couldn’t pass something like that today.”

So what exactly does the act do, and how likely is Trump to be able to use it as promised?

What’s the purpose of the Alien Enemies Act?

The Alien Enemies Act specifically allows the president to detain, relocate, or deport non-citizens from a country considered an enemy of the U.S. during wartime:

“Whenever there shall be a declared war between the United States and any foreign nation or government … and the President of the United States shall make public proclamation of the event, all natives, citizens, denizens, or subjects of the hostile nation or government, being males of the age of fourteen years and upwards, who shall be within the United States, and not actually naturalized, shall be liable to be apprehended, restrained, secured and removed, as alien enemies.”

Congress, with the support of President John Adams, passed the Alien Enemies Act as part of the four Alien and Sedition Acts of 1798 as the U.S. stood on the brink of war with France.

“There was a lot of fear-mongering about French supporters in the United States and about conspiracies to basically get the United States in on France's side,” explains Georgetown University Law Center professor Steve Vladeck.

The controversial group of laws severely curtailed civil liberties, including by tightening restrictions on foreign-born Americans and limiting speech critical of the government.

After President Thomas Jefferson was elected in 1800, he either repealed or allowed most of the acts to expire, except for the Alien Enemies Act, which does not have an expiration date.

It not only remained on the books but continued to expand in scope: Congress amended it in 1918 to include women.

When has the act been used before?

The Alien Enemies Act has been used three times in American history, all in connection with major military conflicts.

During the War of 1812, all British nationals living in the U.S. were required to report information including their age, length of time in the country, place of residence, family description and whether they had applied for naturalization.

A century later, during World War I, President Woodrow Wilson invoked it against nationals of the Central Powers: the German Empire, Austria-Hungary, the Ottoman Empire and Bulgaria.

According to the National Archives, U.S. authorities used the law to place over 6,000 “enemy aliens” — many of them Germans — in internment camps, with some remaining in detention up to two years after fighting had ended.

The U.S. Marshals Service says it registered 480,000 German “enemy aliens” and arrested 6,300 between the declaration of war in April 1917 and the armistice in November 1918.

Most recently, President Franklin Roosevelt invoked the act after the attack on Pearl Harbor, designating Japanese, German and Italian nationals as “alien enemies” during World War II.

Roosevelt's proclamation required residents from all three countries to register with the U.S. government and authorized the internment of any alien enemy “deemed potentially dangerous to the peace and security of the US.”

By the end of WWII, over 31,000 suspected enemy aliens and their families — including Jewish refugees from Nazi Germany — had been interned at camps and military facilities across the U.S., according to the National Archives. Several thousand of them were ultimately repatriated to their country of origin, either by choice or by force.

Vladeck says the Alien Enemies Act was used to detain mostly Italian and German nationals. The bulk of the more than 100,000 Japanese Americans who were placed in internment camps during the war were U.S. citizens, detained under different legal grounds.

How strong is Trump’s case?

The act hasn’t been invoked since WWII, which Vladeck says is largely because the nature of war has changed over the last eight decades.

The fine print of the act says the president can only take on this authority once Congress has declared war, and — while the U.S. has been involved in plenty of conflicts over the decades — it hasn’t done so formally since 1942.

“It hasn't been a source of contemporary controversy because we haven't had a declared war,” he explains. “And no one has tried to argue that that invasion or predatory incursion language could be used in any context other than a conventional war.”

Until Trump, that is. The former president — who has a long history of using dehumanizing language against minority groups and political opponents — has repeatedly referred to the influx of migrants to the U.S. as an “invasion” and vowed mass deportations.

But he hasn’t blamed a specific country or conflict that would fall within the scope of the 1798 act, Vladeck says, which is one of the reasons he doesn’t think Trump’s argument will succeed.

Even some anti-immigration advocates in favor of deploying the act acknowledge those key legal challenges.

Defining illegal immigration as an invasion and migrant gangs as foreign nations would be an “uphill climb in federal court,” George Fishman, former deputy general counsel at the U.S. Department of Homeland Security under Trump, wrote last year.

What are some possible outcomes?

Trump doesn’t need the Alien Enemies Act to go after undocumented immigrants, Vladeck says, noting that presidents already have the authority to arrest, detain and remove them.

“The issue that has hamstrung each of the last four presidents, of both parties, has not been legal authority — it’s a lack of resources,” he says. “The federal government doesn’t have the capacity to identify, track down, round up and remove every single one of the 11 million-plus undocumented immigrants in this country.”

One of the primary obstacles is a lack of funding for immigration enforcement, something that lawmakers sought to address in a bipartisan border security bill earlier this year. It would have put $20 billion toward border provisions and implemented several policy changes to adjust and expedite the asylum process.

Senate Republicans blocked the bill after pressure from Trump, which Democratic critics say he did so that he could campaign in part on fixing the chaos at the border.

“The irony that Trump is now trotting out this old, anachronistic statute to solve a problem that he could have solved much more directly and much less controversially, I think it ought not to be lost on the folks who are learning about these authorities for the first time,” Vladeck says.

If Trump were reelected and proceeded to invoke these powers — which he could do unilaterally, unless a majority of the House and Senate were to block him — Vladeck thinks he would be challenged in court immediately and have a tough time defending his case.

“The sort of the notion that the courts would look kindly upon using this kind of authority where, one, he doesn't need it, and two, it would really be a stretch in what is already a pretty controversial legal power, I think is pretty far-fetched,” he says.

Katherine Yon Ebright, counsel with the Brennan Center’s Liberty and National Security Program, says it’s unclear whether courts would intervene to stop the Alien Enemies Act from being used in peacetime.

“The last time the Alien Enemies Act was challenged, in Ludecke v. Watkins in 1948, the Supreme Court upheld President Harry S. Truman’s extended reliance on the law three years after the end of World War II,” she wrote in a legal analysis. “The Court reasoned that the question of when a war terminates and wartime authorities expire is too ‘political’ for judicial resolution.”

On the other hand, she says, a lot has changed since then, including contemporary understandings of equal protection and due process.

Courts and the public have rejected the 1944 Korematsu case that upheld Japanese internment. Congress provided reparations to surviving Japanese Americans and formally apologized for the use of the Alien Enemies Act during WWII. If a president invokes the act again, she says, courts might look at those legal challenges differently — “on the merits instead of categorically deferring to the president.”

But the surest way to prevent the act from being abused, Yon Ebright writes, would be for Congress to proactively repeal it.

Some Democratic lawmakers — Rep. Ilhan Omar of Minnesota and Sen. Mazie Hirono of Hawaii — have tried in recent years by introducing the “Neighbors Not Enemies” Act, which would repeal the Alien Enemies Act, but hasn’t gained traction.

Omar has resurfaced her calls for action in light of Trump’s recent comments, writing on X that “it’s past time we put this xenophobic law in the dustbin of history where it belongs.”