The best disaster movies usually have a scene where terrified New Yorkers scramble desperately to get out of the city to escape approaching doom. Or else disaster has already struck, civilisation has collapsed and tumbleweed drifts up Fifth Avenue towards the escaped lions roaming Central Park. Many citizens of the Big Apple believe there could be just such a calamity approaching early next week in the form of a fresh-faced, 34-year-old politician whose run for New York City mayor could prove just as disastrous for the city and possibly America, too, as any invading aliens or killer virus. Zohran Mamdani,...