Hunkered behind a MacBook decorated with stickers that read "This laptop was brought to you by capitalism" and "TRUMP 2016," Jake Lopez bounces T-shirt slogans off his friend Ian McIlvoy. "Trumplicans," he says, nodding with satisfaction. "I think it'll take off." Lopez is the California director of Students for Trump. Working from his dorm at Westmont College, he helps marshal the thousands of students who are pounding out phone calls, taping up fliers and blanketing Twitter, Instagram and Snapchat in an effort to persuade their peers that Donald Trump is the man. Although vastly outnumbered nationwide by left-leaning classmates chanting...