President Bukele, who labels himself as the "coolest dictator" and a "philosopher king," has built election success and immense popularity on an extreme security policy to combat gang violence in El Salvador, incarcerating large quantities of alleged gang members and securing a massive drop in homicides.

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.