Dan Koh leads the crowded Democratic primary for Massachusetts' 6th Congressional District as the clear frontrunner, with trader consensus reflecting his substantial early fundraising edge, high-profile endorsements from figures including former President Biden, and status as the first candidate to qualify for the September 1, 2026 ballot. The open seat stems from Representative Seth Moulton's decision to challenge Senator Ed Markey in the Senate primary, drawing a field that includes state Representative Tram Nguyen, self-funded challenger John Beccia, and several other lesser-known contenders. Koh's advantages in cash on hand and grassroots organization have solidified his position, while the remaining candidates trail with limited visibility and support. Recent local endorsements and consistent polling leads further reinforce the current market pricing ahead of the primary.