Daniel Goldman

Brad Lander, the New York City comptroller, will announce on Wednesday that he will challenge Representative Daniel Goldman, setting up a contentious Democratic primary that will be a potent test of the progressive movement’s momentum.

Mr. Lander, who is backed by Mayor-elect Zohran Mamdani, hopes to capitalize on the left-leaning roots of the district, which overwhelmingly supported Mr. Mamdani, a democratic socialist, in November. Mr. Lander is also expected on Wednesday to announce the endorsements of Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont; the left-leaning Working Families Party; and Jumaane Williams, the city’s public advocate.

Mr. Goldman narrowly won the seat, which covers the southern part of Manhattan and parts of Brooklyn, in a crowded primary in 2022. He has drawn praise for sharply questioning Trump administration officials, but his more moderate positions on Israel and the war in Gaza have angered left-leaning constituents.

Mr. Lander said in an interview that voters wanted an even stronger voice to oppose President Trump, to fight for immigrant rights and to help Mr. Mamdani in Washington.

“New Yorkers want Congress members who will step up and fight back against Trump and work with the mayor for a city that everyone can afford and where everyone is welcome,” he said. “Our mayor needs an ally in Washington, and not an adversary.”

Yet Mr. Lander planned to release a campaign video that cast him in a more gentle light, likening him to Fred Rogers from “Mister Rogers’ Neighborhood.” The nearly three-minute video makes use of animated birds flitting across the screen, and ends with Mr. Lander crooning: “Would you be mine? Could you be mine? Won’t you be my neighbor?”

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