A cornerstone of former President Donald Trump's 2024 campaign was his promise to carry out the largest deportation operation in United States history. The details of how he would implement the plan were unclear. But at recent rallies, Trump said he would use an 18th century law to enforce mass deportations.

The deportation operation will begin in Aurora, Colorado, and be called “Operation Aurora,” Trump said at an Oct. 11 rally in Reno, Nevada, adding that immigrants are “trying to conquer us.”

Earlier that day, he said at a campaign rally in Aurora that he would invoke the Alien Enemies Act of 1798 to expedite the removal of gang members and “target and dismantle every criminal migrant network operating on American soil.” “.

Trump was referring to the Venezuelan gang Tren de Aragua, which he said had taken over “several apartment complexes” in Aurora. Claims that a Venezuelan gang had taken over Aurora began in August when a video of a group of Spanish-speaking gunmen walking through an apartment complex in the city went viral. But local officials have pushed back, saying concerns about Venezuelan gangs in Aurora have been “vastly exaggerated.”

Aurora police say they have arrested members of the Tren de Aragua gang, but have not said they took over apartment complexes.

Here's what we know about the 1798 law that Trump promised to invoke, and what legal experts say about Trump's ability to use it for mass deportations.

What is the Alien Enemies Act of 1798?

The Alien Enemies Act of 1798 is part of a larger series of four laws—the Alien and Sedition Acts—that the United States passed out of fear of impending war with France. The laws tightened citizenship requirements, criminalized speech critical of the government, and gave the president additional powers to deport noncitizens.

Three of the laws have been repealed or have been repealed. The Alien Enemies Act is the only one still in effect.

The law allows the president to detain and deport people from an “enemy nation or government” without a hearing if the U.S. is either at war with that foreign country or the foreign country “commits, attempts, or threatens” a legally mandated invasion or raid. has a “predatory incursion” against the USA.

“Although the law was enacted to prevent foreign espionage and sabotage in wartime, it can and has been used against immigrants who have done nothing wrong and are in the U.S. legally,” says Katherine Yon Ebright, an expert on constitutional war powers Brennan Center for Justice, a nonpartisan think tank at New York University School of Law, wrote in an Oct. 9 report for the Brennan Center for Justice.

The law was last enacted during World War II

US presidents have invoked the law three times, only during wartime:

• The War of 1812: Former President James Madison invoked the law against Britons being required to provide information about their age, length of stay in the United States and whether they had applied for citizenship.
• First World War: Former President Woodrow Wilson invoked the law against people from Germany and its allies such as Austria-Hungary.
• Second World War: Former President Franklin Roosevelt invoked the act “to allegedly detain potentially dangerous enemy aliens,” the National Archives said. These included mainly Germans, Italians and Japanese. The law was used to place non-citizens from these countries in internment camps. The law has not been used to incarcerate U.S. citizens of Japanese descent. An implementing regulation was used for this purpose.

Can Trump use the law to carry out mass deportations?

Trump mentioned enforcing the 1798 Act against Mexican drug cartels and Tren de Aragua, the Venezuelan gang.

Legal experts said Trump does not have the authority to use the Alien Enemies Act against gang members or as a tool for mass deportations.

To invoke the law, an invasion must be carried out or threatened by a foreign government. The United States is not currently at war with any foreign government. The law also cannot be generally applied to people from every country.

Invoking the law “as a turbocharged deportation authority … flies in the face of centuries of legislative, presidential and judicial practice, all of which confirm that the Alien Enemies Act is a wartime authority,” Ebright said in her report. “It would be a shocking abuse to invoke this in peacetime to circumvent conventional immigration law.”

Trump and his allies have called the surge in illegal immigration under President Joe Biden an invasion. Legal and immigration experts disagree with the characterization.

Illegal migration or drug smuggling at the southern border is not an invasion, wrote Ilya Somin, a constitutional law professor at George Mason University, in an Oct. 13 report for the online magazine Reason.

Legal experts said an attempt to use the Alien Enemies Act for mass deportations would likely be challenged in court. However, it is unclear whether the courts would make a decision.

The last time a court heard a case involving the Alien Enemies Act was after World War II. Former President Harry Truman had continued Roosevelt's invocation of the law years after the war's end. At that time, the court ruled that whether a war ended and whether war powers had expired were “political questions” and that it was therefore not for the courts to decide.

Similarly, some courts have previously stated that the definition of an invasion is also a political question.

Trump has already promised mass deportations.

During his 2016 presidential campaign, Trump promised to deport all immigrants living in the United States illegally. However, he did not succeed in this.

When Trump took office, an estimated 11 million people were in the country illegally, according to Pew Research. In fiscal years 2017 to 2020, the Department of Homeland Security recorded 2 million deportations. (Fiscal year 2017 covered about four months of former President Barack Obama's term.) By comparison, Obama carried out 3.2 million and 2.1 million deportations in each of his terms, respectively.

The Migration Policy Institute, a nonpartisan think tank, reported in June that the Biden administration had carried out 4.4 million deportations, “more than any single presidential term since the George W. Bush administration (5 million in its second term).”

Steve Vladeck, a constitutional law professor at Georgetown University, wrote in his Oct. 14 newsletter that immigration laws already exist that allow deportations. However, a key obstacle to carrying out mass deportation is the lack of resources required to find, detain and deport large numbers of people.

“Reliance on an old law will not help solve the resource problem,” Vladeck said. ​