New York’s mayor-elect, Zohran Mamdani, is officially backing comptroller Brad Lander in the Democratic primary for New York’s tenth congressional district. Mr. Lander is challenging the incumbent Democrat, two-term Congressman Dan Goldman. 

Mr. Lander is considered to have been a key ally for Mr. Mamdani when he was running for mayor over the course of the last year. In the final days of that Democratic primary, Messrs. Mamdani and Lander endorsed each other to be the other’s number two pick on their respective ranked-choice ballots. 

After Mr. Mamdani won the primary, Mr. Lander could hardly contain his excitement. “Andrew Cuomo is in the past. He is not the present or future of New York City,” he said on the night of the primary election with a wide smile. “Good f—ing riddance.”

After his own defeat, Mr. Lander dedicated his time to helping Mr. Mamdani win the general election. Now that that race is over, he is hoping that left-wing excitement for Mr. Mamdani’s allies can help propel him to a seat in Congress. 

“Brad’s unwavering principles, deep knowledge, and sincere empathy are what make him a true leader,” Mr. Mamdani said in a statement Thursday. “He has been a trusted ally and partner of mine and I’m proud to support him as l know he’ll continue delivering for those who need government to show up for them the most.”

“Thrilled to welcome the endorsement of my friend (and NYC Mayor-elect) @ZohranKMamdani as we continue to fight for the city that we love,” Mr. Lander wrote in response. 

Mr. Mamdani carried Mr. Goldman’s district — which includes the southern tip of Manhattan and portions of Brooklyn — in the Democratic mayoral primary this summer, winning it by more than 35 points. Mr. Goldman declined to endorse Mr. Mamdani in the general election for mayor. 

Mr. Goldman’s campaign did not immediately respond to a message from the New York Sun seeking comment about the endorsement. 

The Working Families Party and a host of other left-wing figures have already backed Mr. Lander. “He has been a leader for all NYers, fought for paid sick leave, and shepherded one of the largest affordable housing projects in years,” the WFP said in a post on X on Wednesday. Senators Bernie Sanders and Elizabeth Warren are also supporting his campaign. 

Mr. Goldman won a hotly contested Democratic primary for the seat back in 2022, after new congressional maps were drawn following the census. He came in first in a field of 12 candidates, winning by just 1,300 votes out of more than 6,000 cast — a margin of just two percent. 

The runner-up in that race, state assembly member Yuh-Line Liou, launched a campaign to challenge Mr. Goldman again in the Democratic primary last year, though she dropped out of the race to allow the liberal base of the party to coalesce around Mr. Lander. 

“While I would be well-positioned to win in a head-to-head race against the incumbent, the division of having multiple candidates on the left only helps the opponents of change,” she said in a statement Tuesday. “We can’t afford that outcome.”

Mr. Lander’s disagreements with Mr. Goldman — like many other Democratic primary challengers to incumbents across the country — has less to do with policy and more to do with position.

One of Mr. Lander’s catchphrases for the race is that Democrats in Congress need to be ready to “fight, not fold.” He was arrested over the summer by federal agents while accompanying an immigrant to an asylum court hearing, as law enforcement tried to detain the person who was going through the legal process to stay in the United States.