On Saturday, Donald Trump led a rally of supporters to raise their right hands and take a pledge that they would vote for him. “Let’s do a pledge. Who likes me in this room?” Trump asked the crowd at a rally in Orlando, Florida, which was frequently interrupted by protesters. “I’ve never done this before. Can I have a pledge? A swearing? Raise your right hand.” The Republican presidential front-runner then proceeded to get the audience to repeat after him. “I do solemnly swear that I, no matter how I feel, no matter what the conditions, if there are hurricanes or...