Bill de Blasio, New York’s left-wing mayor, has suspended his presidential campaign. Michael Bloomberg, the billionaire ex-mayor, is thinking of plunging into the presidential race, on the calculation that none of the present Democratic candidates seem sufficiently “well positioned” to defeat President Trump. And Mr. Trump—a New Yorker if ever there was one—has filed paperwork to change his legal residence from the Trump Tower on Fifth Avenue to Mar-a-Lago, his Xanadu in Palm Beach, Fla.

New York has a multiple personality....