Mamdani's slate of candidates with ties to the Democratic Socialists of America swept out area incumbent Democrats in a stunning win for the 34-year-old mayor.
Former New York City Comptroller Brad Lander unseated Representative Dan Goldman in a Lower Manhattan-area district, Assembly member Claire Valdez defeated Brooklyn Borough President Antonio Reynoso in an open seat being vacated by retiring Representative Nydia Velazquez. Activist Darializa Avila Chevalier narrowly defeated Representative Adriano Espaillat, a five-term congressman and head of the Hispanic Caucus.
All three are expected to win their elections in November, potentially complicating House Democratic Leader Hakeem Jeffries' role as the likely next speaker if Democrats win control of the House of Representatives.
In addition to New York, Maryland and Utah both held primaries on Tuesday, in addition to a gubernatorial runoff in South Carolina.
Three Mamdani-backed candidates won their House primaries, increasing the clout of the Democratic Socialists of America, which now claims several members of Congress, and expanding their influence over the left flank of the Democratic Party.
Mike Marinella, a spokesman for House Republicans' campaign arm, called Tuesday "the night the Democrat establishment officially surrendered to Zohran Mamdani and the socialist wing of their party."
New York Democrats elevated combat veteran and national security expert Cait Conley, a member of the "Hellcat" group of female veterans running for office, to run against Republican Representative Mike Lawler in New York's 17th, a swing district targeted by Democrats.
Lawler is considered the most vulnerable Republican in Congress, representing a district Democratic nominee Kamala Harris won in the 2024 presidential election, though Lawler has consistently performed well, twice winning a district that leans Democratic.
While the current political environment favours Democrats nationally, Lawler will begin the general election with a $US3 million cash advantage over Conley.
Assembly member Micah Lasher beat Assembly member Alex Bores in the crowded primary for the Democratic nomination to succeed retiring Representative Jerry Nadler in New York's 12th Congressional District.
Kennedy scion Jack Schlossberg was a distant third, ahead of George Conway, a former Republican lawyer turned Trump critic whose ex-wife advised the president during his first term.
Lasher will be the overwhelming favourite to be elected to Congress in November.
Trump's first pick in the South Carolina governor's race lost Tuesday's runoff. Lieutenant Governor Pamela Evette trailed Attorney General Alan Wilson by more than 30 points when the race was called about a half hour after polls closed.
Evette finished first in the initial June 9 primary but trailed Wilson in every runoff poll by double digits. Two of Trump's endorsed gubernatorial candidates lost the Republican nomination this month in Iowa and Georgia. But Trump can still claim to have backed the winner in South Carolina.
Wilson is favoured to be elected governor in November. He will face Democratic state Representative Jermaine Johnson in a state Trump carried by 18 points in 2024.
