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.

President Nayib Bukele has offered to jail deported criminals from the United States. His prisons have earned him a reputation as being tough on crime, but have raised alarms over rights abuses.

The Trump administration and the president of El Salvador said Monday that they'd struck a deal allowing the U.S. to ship both detained migrants and imprisoned citizens to the tiny Central American nation,