Mayor Zohran Mamdani stood outside Ken Griffin's $238 million Manhattan penthouse in April and declared victory. "When I ran for mayor, I said I was going to tax the rich. Well, today we're taxing the rich," he said in a social media video marking the debut of New York City's first pied-à-terre tax, an annual fee on luxury properties worth more than $5 million whose owners do not live in the city full time.