At a private home in the West Village on Tuesday evening, a cryptocurrency billionaire, a Qualcomm heir and a son of George Soros hosted a sold-out fund-raiser for Zohran Mamdani, New York City’s incoming mayor. The next morning, Mr. Mamdani was off to TriBeCa, where a Hunt oil fortune heiress and a major cryptocurrency advocate held another fund-raiser for the mayor-elect. Next week, he is slated to appear at a star-studded reception on the Lower East Side featuring Hollywood royalty, including Julianne Moore, Mark Ruffalo, Ramy Youssef, Tituss Burgess and the director Mira Nair, who is Mr. Mamdani’s mother. The...