Dan Koh, a former Biden administration official, won the Democratic primary for Massachusetts' 6th Congressional District on Tuesday, finishing first among six candidates vying to succeed Rep. Seth Moulton, D-Mass., who chose not to seek re-election.
Koh had the backing of both former President Joe Biden and former Vice President Kamala Harris. He previously served as chief of staff to then-Labor Secretary Marty Walsh before becoming deputy assistant to the president and deputy director of the White House Office of Intergovernmental Affairs. The win positions Koh as the heavy favorite in November in a district rated safe blue.
This marks Koh's second bid for federal office. In 2018, he narrowly lost the Democratic nomination for Massachusetts' 3rd Congressional District to Rep. Lori Trahan, D-Mass., by fewer than 100 votes after an extended count.
Moulton, who served four terms representing the district since 2015 and is a Marine Corps veteran, instead pursued the Senate seat held by incumbent Ed Markey. Moulton's Senate campaign focused on generational change, arguing that Markey, 80, had been in office too long to deliver meaningful results for Massachusetts residents.
The strategy did not succeed. Markey won re-election to the Senate, with backing from prominent progressive figures including Rep. Alexandria Ocasio-Cortez, D-N.Y., and Sen. Bernie Sanders, I-Vt.
What the Right Is Saying
Republicans have already positioned for the race. Micah Jones, a military veteran, is running unopposed in the Republican primary and will face Koh in November. National Republicans are expected to contest the seat, though Massachusetts' 6th Congressional District has historically favored Democrats.
Conservative critics argue that Koh's alignment with Biden and Harris could be liability in a political environment where some voters have expressed frustration with the current administration. The district includes portions of Essex County and the North Shore region.
What the Left Is Saying
Progressives note that Koh ran on traditionally liberal platforms, including calls to abolish Immigration and Customs Enforcement and establish universal healthcare. His campaign embraced policies aligned with the broader Democratic Party platform rather than more moderate positions.
However, some progressive groups had backed other candidates in the primary. The Squad and its allies focused their support on Markey's Senate campaign instead, where they successfully defended the incumbent against Moulton's challenge.
Koh's family political legacy may also resonate with establishment Democrats. His father, Howard Koh, served as assistant secretary at the Department of Health and Human Services under former President Barack Obama. A paternal uncle held positions in both the Clinton and Obama administrations.
What the Numbers Show
Moulton's Senate primary performance against Markey reflects broader patterns in Massachusetts Democratic politics. Markey received 66 percent of the vote to Moulton's 34 percent, according to preliminary returns. The margin was consistent with pre-election polling that showed Markey maintaining a comfortable lead throughout the campaign.
Koh's first-place finish in the six-person congressional primary gives him an open path to the House. No Republican has won the district since before World War II. In recent presidential elections, the 6th District voted for Democratic nominees by margins exceeding 20 percentage points.
The seat became vacant when Moulton declined to seek re-election after launching his Senate bid. He served six terms in Congress after first winning election in 2014.
The Bottom Line
Koh's victory sets up a transition from one generation of Massachusetts Democrats to another, with Moulton's departure ending an eight-year House tenure. Republicans will have the opportunity to mount a general election candidate against Koh, but historical voting patterns in the district make the race heavily favoring the Democratic nominee.
The outcome also concludes Moulton's political career at the federal level after his Senate campaign fell short despite significant media attention and his emphasis on national security experience as a Marine Corps veteran who served multiple deployments. What happens next for Moulton remains unclear, though he has not announced plans for future electoral office.
Voters in the 6th Congressional District will cast ballots in November to determine whether Koh, now the Democratic nominee, or Jones becomes their representative in Congress.