Serial fabulist Santos had previously vowed to quit the Big Apple if Mamdani won. In a new video posted on social media, a visibly angry Santos fumed over the result before signing off with: “Good luck, New York. It was nice knowing you. After 37 years, I’m out.”

Zohran Mamdani, the 34-year-old democratic socialist whose focus on working-class issues and personal magnetism attracted a diverse coalition of supporters to propel a once-underdog campaign, has won...