Democrat Analilia Mejia won a New Jersey special election for the US House on Thursday, defeating Republican Joe Hathaway on a message of standing up to Donald Trump.

Mejia, a former head of the Working Families Alliance who had support from the senator Bernie Sanders, will fill the seat previously held by the Democratic governor Mikie Sherrill and serve until January.

Her victory is a win for progressives and means Democrats hold on to the 11th district seat in the House, where Republicans hold a thin majority. It also adds to a string of victories for Democrats heading into this year’s midterm elections.

The Associated Press called the race for Mejia minutes after the polls closed.

Mejia emerged from a crowded primary in February and cast the race as a test of Trump’s leadership. She criticized his pardons of people convicted of January 6-related crimes and faulted him for freezing funds authorized by Congress.

“The people here are ready to do something about it,” she said recently. “We’re not here to write strongly worded letters. Congress has real power.”

She campaigned on populist economic policies and pushing to abolish US Immigration and Customs Enforcement. She has criticized the Israeli government and said she stands with Palestinian communities in their “pursuit of peace and dignity”.

Hathaway tried to use Mejia’s progressive credentials to his advantage, as national Republicans cast her as a socialist.

“I’m running to bring common-sense leadership to D.C + deliver results for our families, not push a far-left agenda,” Hathaway said in a recent social media post.

They could go head to head again in November’s election for a full two-year term.

The 11th district, which covers parts of Essex, Morris and Passaic counties in northern New Jersey’s wealthy suburbs, was long a Republican stronghold but has become increasingly Democratic since Trump’s first term.

Sherrill first won the seat in 2018’s midterm elections, when Democrats flipped dozens of seats to take control of Congress. In 2024, she won re-election by about 15 points, while Kamala Harris, the Democratic presidential nominee, carried the district by nearly nine points.

Saran Cunningham, an 86-year-old retired special educator, said she was initially reluctant to support Mejia, worried that her views were too far to the left. She backed another candidate in the primary. But recently, outside the Morristown early polling location, she said she would now vote for Mejia.

“I think we’ve been tilting a little bit more to the right lately, which worries me,” Cunningham said. “I think that we need people in Congress who will fight for things that will help people as opposed to hurting them.”

Over the years, Mejia has been a regular presence in the state capitol, advocating for progressive causes, and was Sanders’s political director during his 2020 presidential run. During the Biden administration, she was deputy director of the labor department’s women’s bureau. In addition to winning Sanders’s endorsement, she was backed by the US representative Alexandria Ocasio-Cortez and the senator Elizabeth Warren.