President Trump says he’s using the 227-year-old law to crack down on Venezuela’s Tren de Aragua gang. The move is already facing a legal challenge. Here’s a look at key questions and answers about the Alien Enemies Act.

The act is a sweeping wartime authority that allows noncitizens to be deported without being given the opportunity to go before an immigration or federal court judge.

A federal judge barred the Trump administration Saturday from carrying out deportations under a sweeping 18th century law that the president invoked just hours earlier to speed removal of Venezuelan gang members from the United States.