Zohran Mamdani trailed Andrew Cuomo, the frontrunner to be the next New York City mayor, by 30 points just a few months ago. Now, just ahead of the Democratic primary on Tuesday, the 33-year-old democratic socialist has bridged the gap with Cuomo, a politician so of the establishment that a giant bridge north of New York literally bears his last name. The surge in support for Mamdani, an aspiring rapper turned state politician, with a penchant for turning out snappy social media videos and a track record of progressive, leftwing ideas, has shown his clear ability to win over young...