Dan Koh holds a commanding position in the Massachusetts 6th Congressional District Democratic primary due to his early fundraising dominance, exceeding $3.5 million, and the May 2026 endorsement from former President Biden, a former aide to the candidate. The open-seat contest, triggered by Representative Seth Moulton’s Senate primary challenge against Ed Markey, features a fragmented field of state legislators, local officials, and first-time candidates. Koh’s established network and broad donor base have consolidated trader support at 80 percent, while lower-probability options such as Tram Nguyen and John Beccia draw from narrower geographic or self-funded constituencies. With the September 1 primary still months away, ballot access milestones and ongoing campaign events continue to shape the race’s trajectory.