Dan Koh leads the MA-06 Democratic primary market at 78.5% amid a crowded field for the September 1, 2026, contest to replace retiring incumbent Seth Moulton. Koh benefits from superior fundraising, prior congressional experience in the neighboring district, service as a White House official, and recent internal polling showing a 19-point advantage over rivals. State Representative Tram Nguyen trails at 12.9% after stronger early positioning in spring surveys but has seen support consolidate less effectively as the primary nears. The remaining candidates, including John Beccia and lower-polling entrants, face limited visibility and resources. Candidate forums in early August and calls for additional debates have not altered the frontrunner's trajectory in trader assessments.