One social media user wrote that the hedge fund executive Bill Ackman “went from acting like Mamdani was going to import ISIS to extending a friendly handshake… in like six hours.”

. . . Hedge fund manager Bill Ackman poured over $1.75 million into the mayor’s race with a laser focus on stopping Mamdani, whom he often ambushed with several-thousand-word screeds on his X account, which boasts nearly 2 million followers. He accused Mamdani—a staunch critic of Israel—of “amplifying hate” against Jewish New Yorkers, while suggesting that his followers (which happened to include many Jewish New Yorkers) were “terror supporters.”

Meanwhile, the billionaire suggested that the democratic socialist Mamdani’s “affordability” centered agenda, which includes increasing taxes on corporations and the city’s wealthiest residents to fund universal childcare, free buses, and a rent freeze for stabilized units, would make the city “much more dangerous and economically unviable,” in part by causing an exodus of billionaires like himself.

In turn, Mamdani often invoked Ackman’s name on the campaign trail, using him as the poster boy for the cossetted New York elite that was almost uniformly arrayed against his candidacy. In one exchange, Mamdani joked that Ackman was “spending more money against me than I would even tax him.”

After Mamdani’s convincing victory Tuesday night, fueled in large part by his dominant performance among the city’s working-class voters, Ackman surprisingly did not respond with “the longest tweet in the history of tweets” to lament the result as some predicted. Instead, he came to the mayor-elect hat in hand.

“Congrats on the win,” he told Mamdani on X. “Now you have a big responsibility. If I can help NYC, just let me know what I can do.”