Dan Koh leads the Democratic primary for Massachusetts’ 6th Congressional District at 75.5% implied probability due to his substantial early fundraising edge, exceeding $3.5 million, combined with multiple local endorsements and being the first candidate to secure ballot access through petition signatures. The open seat, vacated after incumbent Seth Moulton launched a Senate bid, has drawn a crowded field including state Representative Tram Nguyen and self-funded challenger John Beccia, though neither has matched Koh’s resource or organizational momentum ahead of the September 1 primary. Traders appear to view Koh’s advantages in a low-turnout primary environment as decisive, with limited recent polling or developments altering that assessment.