A vigil at Manhattan’s Union Square to remember the 1,200 Jews killed during the Oct. 7 Hamas attack on Israel three years ago was thrown into chaos Wednesday when pro-Palestinian demonstrators swarmed the plaza, squared off with mourners and blasted Mayor Mamdani, who briefly attended the service.Waving Palestinian flags and screaming “Normalize the intifada!” and “There is only one solution… Revolution!” more than 200 pro-Gaza demonstrators began taking over the seats set aside for attendees at the 7 p.m. vigil. There were four times as many protesters as the 50 who attended the vigil, which was organized by Israelis for...