An overhaul of the U.S. immigration system was a central plank of Trump’s 2016 election campaign. He tightened borders, reduced refugee admissions and access to asylum, and instituted a sweeping ban that mostly targeted travelers from majority-Muslim and African nations. He imposed bureaucratic hurdles to curb legal immigration. Trump used tough diplomacy to pressure Mexico and Central American countries to make it more difficult for migrants to travel north to the United States and, in one widely condemned move, separated parents from their children at the southwest border. While he eventually reversed this so-called “zero tolerance” policy, some separations continued and some parents of separated children have not been located. Under a later policy, almost all migrants seeking refuge at the U.S. border were denied entry and forced to wait in Mexico, pending the outcome of asylum applications that could take months or years. He diverted billions of dollars in military funds to pay for a wall on the southern border that he had vowed during his campaign to have Mexico pay for. Nearly four years on, the wall remains incomplete.