He’s taking a left hook.

State Democratic Chairman Jay Jacobs’ refusal to back socialist Zohran Mamdani’s mayoral bid is turning the party’s ideological rift into a full-blown crater — as lefties call on the longtime boss to resign and moderates hail his “common sense” take.

Moderate mayoral candidates Eric Adams, the incumbent, and Andrew Cuomo, the former thrice-elected Democratic governor, were among those praising Jacobs on Friday for standing up to Mamdani’s radical views.

But support from the pair – who are Dems running as independents – was arguably lost in the progressive blowback against Jacobs for bucking newfound Mamdani backer Gov. Kathy Hochul and failing to endorse the party’s nominee in the nation’s largest city.

“Disgraceful. The Chair of the Democratic Party refusing to support the candidate clearly selected by the voters of the Democratic Party,” state Sen. Michael Gianaris, a progressive, posted on X.

“If he won’t perform that most basic responsibility of a party leader, what exactly is he doing over there?”

State Sen. Kristen Gonzalez and other democratic socialists, were more blunt.

“Jay Jacobs should resign,” she wrote on X.

His refusal to get behind rising star Mamdani — which Jacobs announced in a pointed statement Thursday slamming the Democratic Socialists of America platform — was only the latest gripe many Dems had against him, sources said.

Progressive Empire State Democrats have long been unhappy with Jacobs’ leadership, arguing his mild-mannered approach failed to fire up voters and blaming him for the party’s poor showing in the 2022 midterm elections.

Mamdani, who had signed onto a 2022 letter from lefty Dems calling for Jacobs’ ouster, didn’t join the resignation calls during a Manhattan event with state Senate Majority Leader Andrea Stewart-Cousins, one of his most prominent backers.

The Queens assemblyman said Jacobs’ fate was in Hochul’s hands. But he questioned Jacobs’ stance that he was too alienating for moderates, given his stunning Democratic primary win and gains among voters that previously went for President Trump.

“It’s a coalition that we’re building that has room for everyone, and I think that someone who cannot see that is out of step with the future that we need to be building,” Mamdani said.

“Not just for this party, but for the city and the state.”

How Jacobs’ anti-Mamdani stance will affect state Democratic Party resources flowing into the mayoral race remained unclear, but it laid bare the divides over the party’s overall direction.

“Jay Jacobs is actively undermining party unity and spitting in the face of Gov. Hochul, who’s been notably good to him given the controversy he’s attracted in recent years,” said Chris Sosa, a Democratic consultant and county party committee member.

“This divisive, selfish distraction from the state party chair is the last thing Hochul and Mamdani need to have on their plate right now.”

Mamdani, while a phenom at energizing young voters, struggled to gain endorsements from many prominent New York Dems, such as House Minority Leader Hakeem Jeffries and Senate Minority Leader Chuck Schumer.

He has nabbed the backing of prominent progressives New York Rep. Alexandria Ocasio-Cortez and Vermont Sen. Bernie Sanders, putting the spotlight on the establishment Dems’ silence.

The dam appeared to break when Hochul, a moderate, dropped her endorsement this week, before state Assembly Speaker Carl Heastie came out pro-Mamdani.

She acknowledged her disagreements with Mamdani as she endorsed him, but argued his focus on affordability and potential to fight President Trump made him the clear pick.

Insiders noted her support of Mamdani could help her gain credibility among progressives as she faces a primary challenge from her left flank in next year’s gubernatorial primary.

But Jacobs’ non-endorsement aligns with many in the center of the party, including his fellow Long Island Democrats Reps. Tom Suozzi and Laura Gillen, who oppose Mamdani’s criticism of Israel and unapologetic socialism both on principle and as potentially alienating for moderate voters.

Jacobs also drew praise from Adams, who issued a pointed statement Friday decrying the party’s leftward swing, while seemingly taking aim at Hochul for her endorsement of Mamdani.

Without naming Hochul, Adams — who is polling nearly 40 points behind Mamdani in the November mayoral race — bitterly complained about the “troubling” support the radical Democratic nominee has received.

“At a time when our party must be focused on safety, opportunity, and keeping New York strong, it is deeply troubling to see support given to Zohran Mamdani — a politician whose reckless rhetoric and dangerous policies threaten to divide our communities,” Adams said.

“Mr. Mamdani’s refusal to embrace the internationally recognized IHRA definition of antisemitism, his past tolerance of extremist slogans, and his radical economic vision are not just out of step with mainstream Democrats — they are harmful to the very values that make New York strong.”

The mayor applauded Jacobs’ “independence” and offered his full support for him staying on as chair.

“Jay Jacobs’ leadership is critical to keeping the Democratic Party rooted in common sense, rejecting the march toward socialism, and ensuring that extremists do not hijack our values,” Adams said.

Cuomo, who as governor had appointed Jacobs to his post in 2019, said he couldn’t recall a time when the Democrats’ chair crossed the governor on endorsing a Big Apple mayoral nominee.

“It clarifies the situation,” Cuomo, who was thoroughly trounced by Mamdani in the June Democratic primary, said Thursday during a campaign event in Staten Island.

“The Democratic Party chairman did not endorse Mamdani — why? Because he is not a Democrat. He is a socialist. He is a socialist who ran and won in a Democratic primary. Socialists and Democrats are apples and oranges.”

Democratic political operative Ken Frydman said Jacobs has no one to blame but himself for the progressive revolt.

“Shame on him for giving away the left flank,” Frydman said. “He dropped the ball. He’s supposed to register voters. It’s a business.

“Either fall on the sword or be fired. (The party) should have seen it f—ing coming.”

One party source pointed out that some were already generally dissatisfied with Jacobs’ leadership, believing that him spending his summer running summer camps showed he lacked the energetic focus to win.

“There’s a huge group that isn’t on his side that thinks he’s a weak leader,” the source said.

– Additional reporting by Carl Campanile