"MOM, WHY ARE YOU STILL AT WORK?” Ms. Akhtar’s 24-year-old son, Humza Mehfuz, wrote to her. “YOU HAVE TO VOTE!” While Ms. Akhtar had previously supported Mr. Mamdani’s main opponent, Andrew M. Cuomo, when he ran for governor and, years before that, had voted for his father, former Gov. Mario Cuomo, she told her children to calm down. After their relentless campaign of showing her TikTok videos of Mr. Mamdani — “This kid is brilliant,” she had to admit, “and so friendly!” — she had made her decision. “All of Cuomo’s ads tried to make Mamdani look like a terrorist,”...