New York Mayor Zohran Mamdani and key allies secured major wins in Tuesday’s congressional primaries as they looked to build on his 2025 victory by expanding the power and presence of the democratic socialist movement in Washington.

Former New York City Comptroller Brad Lander dethroned Democratic Rep. Dan Goldman in the Democratic primary for New York’s 10th District without much tension Tuesday, the first victory for the Mamdani-backed slate. Lander captured about two-thirds of the vote.

Soon afterward, NBC News projected that state legislator Claire Valdez had defeated Brooklyn Borough President Antonio Reynoso in the open 7th District, where longtime Rep. Nydia Velázquez is retiring. Velázquez — and a number of prominent city political leaders — backed Reynoso, who leaned on his relationships in Brooklyn and his record on issues like police reform.

But they were no match for Mamdani and other allies, who elevated Valdez, 36, a first-termer in the state Assembly who moved to the city in 2015. She ran a hard-charging campaign calling for “Medicare for All” and a “public option for housing.” And she argued she was a stronger advocate than Reynoso in their approaches to criticizing Israel’s conduct in its war against Hamas.

Then, Darializa Avila Chevalier — another young democratic socialist and community activist whose campaign flew under the radar before Mamdani endorsed her — defeated 10-year Rep. Adriano Espaillat, chairman of the Congressional Hispanic Caucus.

Other dynamics in play in Tuesday’s primaries across four states included tens of millions of spending from super PACs funded by the artificial intelligence industry, pro-Israel groups and a pair of wealthy Democrats engaged in a knock-down, drag-out primary in Maryland.

But the success of the Mamdani-led power play across New York was the biggest news of the night.

“Tonight it became clear that the old guard of New York City politics it’s just that, old,” tweeted Joe Calvello, Mamdani’s chief spokesperson.

The districts, spread out across three of the city’s boroughs, share some similarities. All three are among the city’s most rapidly gentrifying neighborhoods, with Valdez herself a somewhat recent transplant to her district. All three are also among the districts where Mamdani performed the strongest in his mayoral election last fall against former Democratic Gov. Andrew Cuomo.

The victories follow other contested primary wins for upstart progressive and socialist campaigns in recent months, including veteran and oyster farmer Graham Platner in the Maine Senate primary, Randy Villegas in a California swing district, state Rep. Chris Rabb in a blue district in Philadelphia, and Adam Hamaway and Rep. Analilia Mejia in a pair of New Jersey districts. In other contests, left-aligned candidates Abdul El-Sayed and Lt. Gov. Peggy Flanagan are top contenders in Democratic Senate primaries in Michigan and Minnesota, respectively.

“It’s a big night for sure,” Rebecca Katz, a prominent Democratic strategist and ally whose firm worked with Mamdani during his 2025 run, said of the Mamdani-backed candidates sweeping Tuesday. “The energy is there, but every congressional district is different. To win in November, Democrats must embrace candidates who can authentically speak to the electorate they’re running to represent.”

For Mamdani, the results represent a significant return on investment of his political capital, after he endorsed against a close ally in one race and went back on a promise not to jump into another. The mayor campaigned hard for the candidates he backed, appearing in person with them during the final days of the contests and cutting an ad alongside them where he branded the slate as his “team.”

The victories are part of a democratic socialist effort to prove the durability of their movement and redefine what it means to be a progressive in the modern Democratic Party.

Fiery debates over Israel policy defined all three races, as the challengers all sought to speak to the growing group of Democrats who soured on Israel amid its war with Hamas in Gaza. All three called Israel’s conduct “genocide” and made the issue an important piece of their campaign.

Meanwhile, their opponents pointed to what they argued were important progressive victories they helped achieve in recent years. Goldman served as lead counsel during Trump’s first impeachment, Reynoso helmed the city council’s Progressive Caucus, and Espaillat is a former undocumented immigrant who has pressed the Trump administration on immigration.

But their challengers argued that it’s not enough for Democrats to cling to the old model of what it means to be a progressive at this pivotal moment — not just as Trump and Republicans control all of Washington, but as the cost of living continues to loom large on voters’ minds.

Races in other competitive primaries did not experience the same shocks on Tuesday. While the shared political DNA of these New York districts helped create fertile ground for anti-establishment campaigns drafting off Mamdani’s success, other forces remained influential in other places.

In Maryland, where retiring Democratic Rep. Steny Hoyer has represented the 5th District for decades, state Del. Adrian Boafo, a former Hoyer aide, won. There’s no indication that the millions a pro-Israel super PAC spent to boost him did anything but help.

And in Utah’s 1st District, a new Democratic district in Salt Lake City created after courts struck down the congressional lines there, former Rep. Ben McAdams won the primary over a progressive state lawmaker backed by Sen. Bernie Sanders, I-Vt.

Elsewhere in New York City, a dramatic clash between competing visions for AI regulation has drawn tens of millions of dollars into the 12th District. But the winner, Assemblyman Micah Lasher, sidestepped that debate and won the Democratic primary nonetheless.

Lasher has the backing of Nadler, as well as major state party leaders including Gov. Kathy Hochul and former Mayor Michael Bloomberg — who remains popular in the Manhattan district, where older voters play an outsized role in elections. Lasher has worked for all three of those leaders.

Initially, the race looked to be defined either by tech titans spending in response to Assemblyman Alex Bores’ aggressive calls to regulate AI, national attention on a Kennedy family scion or George Conway’s prominent “Never Trump” branding. But ultimately, Lasher leaned on his deep local ties to win the contest.