They are seeing red!

The Big Apple’s commune of radical socialists freaked out after their de facto leader Zohran Mamdani backed outgoing City Comptroller Brad Lander’s congressional bid over one of their own far-left comrades.

Lander formally announced his campaign Wednesday morning to primary Rep. Dan Goldman for New York’s 10th Congressional District — a House seat that had also been eyed by lefty City Council member Alexa Avilés.

Both Mamdani, the incoming mayor, and Avilés are members of the Democratic Socialists of America.

“Crazy maneuvering by Zohran and a complete failure for DSA,” one of the group’s members opined on social media.

“So basically Zohran, a DSA member, is gonna be endorsing Brad Lander, who is not a DSA member, over Alexa Aviles, a DSA member, in NY-10,” another wrote.

David-Desyrée, who sits on the NYC-DSA Citywide Leadership Committee, was also dismayed by Mamdani’s latest move to back Lander.

“I’m so beyond disappointed in zohran for backing lander and sidestepping the organization that got him elected,” Desyréewrote on X.

One DSA member didn’t mince words, writing, “Also f–k Brad Lander.”

Avilés was rumored to be eyeing a Democratic primary challenge against two-term congressman Goldman for the Manhattan seat, but had not formally declared.

She responded to Lander’s campaign announcement — which also came with the backing of fellow socialist Vermont Sen. Bernie Sanders — by bowing out.

“In recent weeks, I have received an outpouring of support from community members encouraging me to run for congress,” she wrote in a statement. “However, after conversations with family and movement, I have decided that there is far too much to be done at home in Brooklyn and at City Hall.

“Thank you to my comrade in the NYC-DSA,” she said. “The fight for a dignified city has only just begun.”

Lander had angled for a spot in the Mamdani administration after the two polls cross-endorsed each other in the final days of the Democratic mayoral primary.

But after a falling out with the mayor-elect, according to sources, Lander set his sights on the congressional seat — with the seeming consolation prize from Mamdani being clearing the field of a challenge from the far-left.

The endorsement, though, could end up dogging Mamdani as he tries to hold together an unstable alliance of moderate, progressive and socialist Democrats.

The lefty Queens assemblyman also went to bat against fellow DSA member Councilman Chi Ossé, who ended up dropping his short-lived bid to primary House Minority Leader Hakeem Jeffries for his Brooklyn seat.