Beth Andres-Beck, John Beccia, Dan Koh, Mariah Lancaster, Tram Nguyen, and Jamie Zahlaway Belsito are running in the Democratic primary for Massachusetts' 6th Congressional District on Sept. 1. Incumbent Seth Moulton (D) is running for the U.S. Senate to represent Massachusetts.

The election is set against the backdrop of affordability and opposing President Donald Trump's (R) administration. When distinguishing themselves, the candidates have emphasized their experience either in or outside of Washington, D.C. Belsito, Koh, and Lancaster have experience in Washington, D.C., and argue that their understanding of the federal system would benefit the district. Tram, a state legislator, says she is the only candidate with current legislative experience. According to The Boston Globe, Andres-Beck and Beccia argue that their non-political backgrounds would provide "fresh, outside perspectives to Capitol Hill."

In coverage of a June 2026 candidate debate, The Boston Globe's Anjali Huynh wrote, "Candidates offered similar, if not identical, messages in different fonts throughout the night, making it feel more like a collaborative policy discussion than a contentious debate. Nowhere was that more prevalent than on issues around affordability ... Proposed solutions included strengthening worker protections (Nguyen), pushing middle-class tax relief (Beccia), reining in housing and child care costs (Koh), breaking up monopolies (Lancaster), reversing Trump’s tariffs (Belsito), and changing federal policy to address education and energy prices (Andres-Beck)."

• Andres-Beck is a senior staff software engineer. Andres-Beck says, "America could have good things: functional healthcare, honest government, safe schools, and a future we can take pride in building. I'm running for Congress because I believe we can have those things, not because we behave or wait our turn, but because we organize, show up, and believe in one another."
• Beccia is the co-founder and chair of FS Vector, a financial services strategic consulting firm. Beccia's campaign website says, "John is tired of politicians making unkept promises and offering the same old solutions that don’t work anymore. He is running for Congress to do what he did in business: create jobs, protect consumers, and make our economy work for working people."
• Koh is the host of The People’s Cabinet podcast and a former chief of staff at the U.S. Department of Labor and senior aide in former President Joe Biden's (D) administration. Koh's campaign website says, "Dan Koh is running for Congress because Donald Trump is trampling our constitution and American way of life, and we need leaders fighting back to defend our Democracy, protect our rights, reduce the cost of living, and stand up for families and communities like ours."
• Lancaster is a veterinarian who previously served as a foreign affairs officer at the State Department, and science policy advisor and legislative staff in the U.S. House of Representatives. Lancaster's campaign website says, "[Lancaster] will keep money in the pockets of hardworking Americans by fighting for universal healthcare, affordable housing, equitable and accessible education, and to keep safe, healthy food on every kitchen table across America."
• Nguyen is an attorney and represents the 18th Essex District in the Massachusetts House of Representatives. Nguyen's campaign website says, "Now Tram is running for Congress to tackle the high cost of living, expand affordable housing, protect fundamental freedoms, and restore trust in our democracy. Tram knows that we don’t have to choose between making life better for people, and standing up to Trump. We can, and we must, do both."
• Zahlaway Belsito is the founder of the Maternal Mental Health Leadership Alliance. Zahlaway Belsito says, "While Trump wages war on our democracy, too many Democrats argue about whether we need to abandon transgender Americans or abortion rights. I'm a Democrat who won't apologize for human rights, universal healthcare, and a fair economy with good union jobs. We don't need to choose between these values, we need to lead on them."

As of July 3, The Cook Political Report with Amy Walter, Inside Elections with Nathan L. Gonzales, and Larry J. Sabato's Crystal Ball rated the district Solid/Safe Democratic.

This is one of 58 races for the U.S. House of Representatives this year in which an incumbent is not running for re-election. Across the country, 22 Democrats and 36 Republicans are not running for re-election. In 2024, 45 incumbents — 24 Democrats and 21 Republicans — did not seek re-election.