When a congressional seat opens up after half a century, political ambition explodes. That is exactly what happened in Massachusetts when U.S. Rep. Seth Moulton vacated the Sixth District seat to launch a Senate campaign. Into that massive vacuum stepped a crowded, chaotic field of Democratic hopefuls.
Former Biden White House aide Dan Koh cut through the noise and captured the Democratic nomination. While other candidates scrambled to distance themselves from national figures, Koh leaned entirely into his executive background and his time in Washington. Voters responded by putting him at the top of a brutal five-way primary race.
Let's look at how this race actually played out on the ground.
Navigating a Crowded Field
The Sixth Congressional District runs all the way from Lynn up through the North Shore to the New Hampshire border. It is a massive swath of Massachusetts that hadn't seen an open seat without an incumbent on the ballot since 1978. That scarcity drew heavy hitters out of the woodwork.
Koh faced state Rep. Tram Nguyen, fintech executive John Beccia, former state Rep. Jamie Belsito, and software engineer Bethany Andres-Beck. The race turned into an expensive, high-stakes sprint. Koh entered primary day sitting on a war chest of roughly $4.7 million, making him the best-funded candidate in the cycle. Much of that financial backing came through major donors in Boston and New York, alongside outside support from political action committees.
Yet money alone doesn't win primaries in the North Shore. Competitors like Nguyen built deep local credibility, pulling in high-profile endorsements from regional leaders and progressive powerhouses as the race entered its final stretch. But Koh maintained a distinct advantage through a network forged during his years working for Boston Mayor Marty Walsh and later inside the Biden administration.
The White House Factor
In modern primary politics, candidates often run away from Washington associations. Koh did the exact opposite. He prominently featured his ties to former President Joe Biden and Vice President Kamala Harris.
Instead of treating his executive branch experience as a liability, Koh framed it as proof that he knew how to deliver results. He campaigned heavily on a platform centered around fighting Donald Trump, protecting democratic institutions, and leveraging federal dollars to help local Massachusetts families. That gamble paid off. High-profile figures and major labor organizations, including the Massachusetts AFL-CIO and local Teamsters chapters, lined up behind his candidacy.
By the time the Associated Press called the race, Koh had secured a commanding lead with roughly 43 percent of the vote, putting him comfortably ahead of Nguyen.
What Comes Next for the Sixth District
Winning the Democratic primary in this part of Massachusetts is basically the whole ballgame. The district leans heavily democratic—the Cook Political Report rates it significantly to the left of the national average.
Koh now advances to the November general election. Given the deep-blue leaning of the North Shore, he enters that matchup as the heavy favorite to succeed Moulton, setting the stage for a potentially long tenure representing a district that has historically kept its representatives for decades.
If you want to track the official vote counts and general election preparations, check the Massachusetts Secretary of the Commonwealth Elections Division for certified municipal returns and district updates.
