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Here's who's running to replace Seth Moulton

Boston.com · August 26, 2026

Six candidates currently remain in the crowded Democratic primary race in Massachusetts’ 6th Congressional District.

After Rep. Seth Moulton announced his plans to challenge Sen. Ed Markey last October, a slew of candidates quickly jumped into the race to fill Moulton’s House seat.

Six candidates currently remain in the crowded Democratic primary race in Massachusetts’ 6th Congressional District. The six candidates come from a wide range of backgrounds, with experience ranging from state politics to the private sector and the classroom.

Five of the six candidates attended a debate in North Andover on July 28 and sparred over issues,including health care costs, money in politics, local infrastructure, and this summer’s Haverhill sewer break. But, they shared common ground on the importance of standing up to the Trump administration and making Massachusetts more affordable for its residents.

The state primary is on Tuesday, Sept. 1, with the winner moving on to face Republican Micah Jones in the general election. Jones is running unopposed in the Republican primary. The candidates are listed below in alphabetical order.

Bethany Andres-Beck

Andres-Beck, a software engineer and democratic socialist from Middleton, was the first candidate to get into the race last summer, with the intention of challenging Moulton before the current congressman announced his bid for Senate. Andres-Beck has framed themselves as a political outsider who will be skilled in fighting corruption. They want to focus on efficient government software, better support for the working class, and universal health care. Andres-Beck, who is themselves transgender, said they want to focus on the country’s most urgent problems, like AI regulation and affordability, rather than “wedge issues,” like transgender athletes in youth sports. Andres-Beck spoke to Boston.com last year about their upstart campaign.

John Beccia

Jamie Belsito

Dan Koh

Koh, an Andover native, served as a senior aide in the White House under the Biden administration and prior to that was chief of staff to former Boston Mayor Marty Walsh. Koh, leaning heavily into his Washington experience, emphasizes his work with Biden’s cabinet implementing legislation focused on investments in infrastructure, clean jobs, education, and lowering prescription drug costs for seniors. This is Koh’s second congressional campaign, after he narrowly lost in the 2018 Democratic primary for Massachusetts 3rd Congressional District against Rep. Lori Trahan. Koh’s campaign highlights clips of him “fighting MAGA in the media,” featuring his regular appearances on CNN, Fox News, and right-wing podcasts. Last year, Koh also offered his commentary on national issues through a YouTube channel “The People’s Cabinet,” interviewing other politicians. Koh missed the July 28 debate due to a death in his family.

Mariah Lancaster

Lancaster, a Salem resident, is a veterinarian who served the past four years as a civil servant in Washington, helping to support progressive policy. Lancaster has experience in the State Department as a foreign affairs officer, and as a congressional aide for Minnesota Rep. Betty McCollum and California Rep. Julia Brownley. Lancaster said they moved into nonprofit work, advocating for public health, conservation, and national security, as a response to Republicans taking control of Congress. A Massachusetts native, Lancaster said they moved back home to “fight” the Trump administration, with a campaign focusing on four key areas: enacting universal health care, fighting corruption, improving access to education, and implementing energy policies that bring down costs. The last candidate to launch their campaign, Lancaster said they joined the race because they were frustrated with the complacency they saw in Washington.

Tram Nguyen

Nguyen, a current state representative, is serving a district that includes parts of Andover, North Andover, Boxford, and Tewksbury. Before being elected to the state Legislature, Nguyen worked as an attorney with Greater Boston Legal Services, where she led a program advocating for people who were victims of crimes. Nguyen flipped a seat held by a Trump-aligned Republican in 2018 to become the first Vietnamese American elected to serve in the State House. Nguyen is calling for an urgent response to the housing affordability crisis, a transition to “Medicare for All,” and a continued fight for our democracy that she says is under attack by MAGA extremism.