WASHINGTON — Late to his own meeting and waving a sheet of numbers, President Trump stormed into the Oval Office one day in June, plainly enraged.Five months before, Mr. Trump had dispatched federal officers to the nation’s airports to stop travelers from several Muslim countries from entering the United States in a dramatic demonstration of how he would deliver on his campaign promise to fortify the nation’s borders.But so many foreigners had flooded into the country since January, he vented to his national security team, that it was making a mockery of his pledge. Friends were calling to say he...