Ackman said he was “gravely concerned” because he believed the left-wing candidate’s policies would be disastrous, triggering an exodus of the wealthy that would endanger New York’s public services by hollowing out its tax base.

“New York City under Mamdani is about to become much more dangerous and economically unviable,” the Pershing Square CEO posted to social media on Wednesday.

Arguing that his own support of President Trump would automatically disqualify anyone Ackman might put forward, the activist investor said he was making a public appeal: Anyone capable of taking down Mamdani in the Nov. 4 election should step forward and volunteer. 

“Funds will pour in”

“Importantly, there are hundreds of millions of dollars of capital available to back a competitor to Mamdani that can be put together overnight (believe me, I am in the text strings and the WhatsApp groups) so that a great alternative candidate won’t spend any time,” he wrote.

“So if the right candidate would raise his or her hand tomorrow, the funds will pour in.”

I awoke this morning gravely concerned about New York City. I thought “What has NYC become that an avowed socialist who has supported defunding the police, whose solution to lowering food prices is city-owned supermarkets, who doesn’t understand that freezing rents will only…

— Bill Ackman (@BillAckman) June 26, 2025

Ackman even alleged Michael Bloomberg, former NYC mayor and billionaire founder of the eponymous financial media company, would lend his entire election apparatus to any aspiring candidate to free them up to campaign rather than organize and fundraise.

It’s unclear whether New Yorkers would honor such a candidate. The recent intervention by Elon Musk in Wisconsin’s state supreme court election indicated the voting public does not always respond well to billionaires using their money to sway races.

Fortune has reached out to the Mamdani campaign for a response.

Exodus of the tax-paying wealthy

In a political earthquake, the charismatic 33-year old outsider thumped the state’s scandal-shrouded former governor, Andrew Cuomo, in the Democratic Party primary on Tuesday after applying a laser-like focus on the cost-of-living crisis for everyday New Yorkers.

While Cuomo relied on name recognition and an extensive political network to out-fundraise his rival nearly four times over, the largely unknown state assemblyman pushed for rent freezes, subsidized city-owned supermarkets, and free public transit—all funded by taxes on local corporations and the wealthy. 

“If 100 or so of the highest taxpayers in my industry chose to spend 183 days elsewhere, it could reduce NY state and city tax revenues by ~$5 -$10 billion or more,” Ackman warned, drawing a comparison to a fellow hedge-fund founder. “Think Ken Griffin leaving Chicago for Miami—on steroids.”

Mamdani overcame repeated attacks about his limited experience in government and his Muslim faith to become the undisputed frontrunner with a convincing victory over establishment-backed Cuomo. The Democratic socialist is currently a heavy favorite in the November election against unpopular incumbent Eric Adams, who is running as an independent, and Curtis Sliwa, the Republican nominee and founder of the Guardian Angels.

Chronically low voter turnout in mayoral races could prove a key advantage

New York mayoral races are notoriously unpredictable due to the city’s chronically low turnout. In 2017, for example, Bill de Blasio won reelection with only 14% of registered voters coming out to support him. 

A large influx of New Yorkers heading to the voting booth because they are as concerned as Ackman could easily affect the outcome. If Cuomo can hold on to enough fundraisers, political pundits also point out, it’s possible he could run as an independent like Adams, splitting the left vote and spoiling the race.

Ackman, however, argued all these factors would support the emergence of a centrist candidate looking to position themself on the national stage. It could even be another businessman like Bloomberg, he suggested, although Ackman in an earlier post appeared to indicate he would not seek to run himself.

“For the aspiring politician there is no better way to get name recognition, build relationships with long-term donors, and to showcase oneself,” the hedge fund manager wrote, pitching the campaign like a business deal. “The risk/reward of running for mayor over the next 132 days is extremely compelling as the cost in time and energy is small and the upside is enormous.”