Brad Lander defeated two-term incumbent Dan Goldman in the Democratic primary for New York's 10th Congressional District on June 23, 2026, capping a sweep by candidates backed by New York City Mayor Zohran Mamdani that removed multiple sitting House members in a single night.

Lander, a former NYC Comptroller, beat Goldman — who had held the Lower Manhattan and Brooklyn district since 2023 — in what Politico characterized as a rout. In the same primary cycle, Darializa Avila Chevalier ousted Representative Adriano Espaillat, another Mamdani-endorsed candidate clearing out a long-standing incumbent. A third Mamdani pick, Claire Valdez, also ran with the mayor's backing, per NBC News.

The NY-10 race turned significantly on Israel policy. Lander, who is Jewish, campaigned as a vocal critic of Israeli military conduct — a posture that separated him sharply from Goldman on the district's defining fault line, according to the New York Times. The district's demographics, spanning progressive enclaves in Brooklyn and lower Manhattan, gave that contrast electoral weight.

Goldman's vulnerabilities had been accumulating. A federal immigration court in New York had become a focal point of the NY-10 contest earlier this year, with Lander making immigration enforcement a live issue in a district where the politics of deportation carry immediate community resonance, per AP. The race also drew controversy in early June when AFP Fact Check reported that Lander shared a video that purportedly altered a clip of Goldman speaking — a notable flashpoint in the closing weeks.

The Mamdani Factor

The collective outcome across these primaries cannot be read apart from Mamdani's political infrastructure. Mamdani won the Democratic mayoral primary in June 2025, defeating ten other candidates, and has since built a cross-district operation aligned with Democratic Socialists of America networks. Reuters noted before polls closed that DSA-affiliated candidates backed by Mamdani were positioned to sweep incumbent Democrats from multiple seats.

That sweep materialized. The pattern — a sitting mayor deploying mayoral-level organizing muscle into congressional primaries — is structurally unusual in New York politics. Mayors typically husband their capital for city business and avoid making enemies in the congressional delegation. Mamdani inverted that calculus entirely.

NY-12 and the Nadler Succession

Elsewhere in the city, Micah Lasher won the Democratic primary for New York's 12th Congressional District, the seat opened by the retirement of veteran Representative Jerrold Nadler, according to the Washington Post and NY1. Jack Schlossberg was among the candidates who had contested that race. Lasher's win closes a competitive open-seat fight that attracted significant attention as one of the few undefended incumbencies on the ballot.

What Comes Next

The general election implications depend heavily on district partisanship. NY-10 and NY-12 are among the most reliably Democratic districts in the country; a Democratic primary win is, in practical terms, the decisive contest. Lander and the other Mamdani-backed winners will be heavy favorites in November.

The more immediate question is what Tuesday's results mean for the balance of power within House Democratic caucus politics. Goldman had been a prominent media presence and a consistent voice aligned with the party's centrist-to-liberal wing. His loss, alongside Espaillat's, thins the ranks of that faction and adds seats that will likely vote with the caucus's left bloc on contested questions — from military aid conditionality to domestic spending negotiations.

Mamdani, barely a year into the mayoralty, now holds a credible claim to having reshaped New York's congressional map. Whether that translates into durable leverage, or whether the incumbents he targeted were simply individually weak in districts that had moved left of them, is the question the next cycle will answer.