Mamdani won a record-setting primary victory, and unions, grassroots Democratic groups, and savvy elected officials are rushing to back him. Now it’s the establishment’s turn.

Mr. Mamdani’s victory upended city politics and reverberated nationally. He relied on a memorable message, charisma and a strong ground game.

Fresh off losing New York’s Democratic primary for mayor to Zohran Mamdani, former Gov. Andrew Cuomo on Monday ramped up his efforts to push the incumbent mayor, Eric Adams, out of the race.