The proposal is almost certainly illegal, experts said, but President Trump’s eagerness to entertain it showed his willingness to embrace extreme measures to demonstrate he is tough on crime.

The Trump administration and the president of El Salvador said they struck a deal allowing the U.S. to ship detained migrants and imprisoned criminals to a mega-prison there

Under U.S. immigration law, a country such as El Salvador can accept someone deported from the U.S. who isn’t a citizen of that country if the person’s homeland refuses to accept them, says Theresa Cardinal Brown, a former homeland security official under the administrations of Presidents George W. Bush and Barack Obama.