A federal judge blocked the Trump administration from removing any migrants under the Alien Enemies Act late Saturday—but the White House said Sunday that hundreds of alleged gang members had still been sent to El Salvador.

The Trump administration said Sunday that hundreds of individuals were deported from the country after President Donald Trump invoked the Alien Enemies Act, a sweeping wartime authority which has been used only three times before,

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.