The chairman of the New York State Democratic Party said on Thursday that he would not support Zohran Mamdani, his party’s nominee for mayor of New York City, citing fundamental disagreements over Israel and democratic socialism.
The position puts the chairman, Jay Jacobs, directly at odds with both Democratic primary voters and Gov. Kathy Hochul, his de facto boss, who endorsed Mr. Mamdani on Sunday despite her own differences with the nominee.
Mr. Jacobs, a moderate from Long Island, was so opposed to the governor’s endorsement that he told associates in recent days that he would sooner resign as chairman than back Mr. Mamdani, a 33-year-old state lawmaker and democratic socialist, according to people who spoke with the chairman.
It appears not to have come to that. But Mr. Jacobs’s exceedingly rare public break with Democratic voters and the governor underscores the deep divisions that persist around Mr. Mamdani within the party’s establishment, even as more elected officials move toward supporting him.
In a statement to The New York Times on Thursday, Mr. Jacobs, who is Jewish, said he told Mr. Mamdani directly that “I strongly disagree with his views on the State of Israel.”
“Furthermore, I reject the platform of the so-called Democratic Socialists of America and do not believe that it represents the principles, values or policies of the Democratic Party,” Mr. Jacobs said.
At the same time, Mr. Jacobs said he respected Ms. Hochul’s decision, pledged not to endorse any other candidate in the mayor’s race and called the “fearmongering” about Mr. Mamdani a “wrong and a gross overreaction.”
A spokeswoman for the governor, who appeared with Mr. Mamdani Wednesday night at a Bronx Democratic Party dinner, declined to comment.
A spokeswoman for Mr. Mamdani did not immediately respond to a request for comment.
Democrats have been at odds over Mr. Mamdani since his surprise victory over former Gov. Andrew M. Cuomo in the primary in June.
The assemblyman excited young voters, progressives and South Asian immigrants, among others, with his populist economic platform, which calls for making buses free, freezing rent on rent-stabilized apartments and expanding free child care.
But his association with the D.S.A., calls for tax increases and sharp criticism of Israel’s war in Gaza alarmed other constituencies the party typically relies on in New York: moderate Democrats, some Jewish voters and the city’s powerful business class.
The decision by Mr. Jacobs — who leads fund-raising, candidate recruiting and key campaign spending decisions for the party — reanimated that fight on Thursday.
The timing was especially notable. Mr. Mamdani has shed or moderated certain left-wing positions over the last several months, and polls show he has a commanding lead in the race. Though there are still several holdouts, Mr. Mamdani has now won endorsements from every top Democratic official in Albany and warm words from Ken Martin, the chairman of the Democratic National Committee. (Mr. Jacobs is also a member of the national committee.)
Christine Quinn, a former City Council speaker who serves as a top state party official under Mr. Jacobs, called his choice a “surprise.”
“It’s hard to have a person hold this perch where they are asking other people to stand with the party when they are not willing to stand with the party themselves,” Ms. Quinn said.
Mr. Jacobs has been in the middle of Democrats’ intraparty fights for years. He has clashed repeatedly with his party’s left wing, which in turn has agitated for his removal as chairman. Tensions had eased after 2024 when he and Ms. Hochul helped build a statewide turnout organization that helped the party flip key House seats.
Charles Lavine, a state assemblyman from Nassau County on Long Island, said Mr. Jacobs, who also leads the local Democratic Party there, has been worried about how the views of Mr. Mamdani and his allies could be used against Democrats running in competitive races in a region that has moved rightward. He cited Representatives Tom Suozzi and Laura Gillen, whose districts include parts of Nassau County and are pivotal to the national fight for Democrats to control the House.
Mr. Lavine also said the chairman had longstanding frustrations with democratic socialists, who he believes have pushed the party too far left, and who have criticized local politicians for taking trips to Israel.
“Jay’s fierceness on this particular issue is in a different class altogether,” Mr. Lavine said.
This is not the first time Mr. Jacobs has declined to endorse a democratic socialist candidate who won a Democratic primary. In 2021, he did not back India Walton after she upset Mayor Byron Brown of Buffalo in that city’s primary. Ms. Hochul, who is from Buffalo, also declined to endorse Ms. Walton, and Mr. Brown later won a write-in campaign.
In the New York City race, Ms. Hochul acknowledged she had differences with Mr. Mamdani in a guest essay published in The New York Times on Sunday announcing her endorsement. But she said they had found common ground over trying to make New York City more affordable.
Ms. Hochul also had her own political standing in mind. She is preparing to run for re-election next year and faces a challenge from her lieutenant governor, Antonio Delgado; Mr. Mamdani could help her shore up support on her left flank.
Mr. Jacobs, who runs summer camps as his day job, was appointed to lead the party by Mr. Cuomo. He stayed on in the role after the former governor’s resignation in 2021, becoming a loyal adviser to Ms. Hochul.