Dan Koh holds the strongest position in the Massachusetts 6th Congressional District Democratic primary, driven by his early fundraising dominance exceeding $3.5 million, a high-profile endorsement from former President Biden in early May 2026, and support from local officials and groups such as End Citizens United. The open-seat contest, following Rep. Seth Moulton’s decision to challenge Sen. Ed Markey in the Senate primary, features a crowded field where Koh’s prior White House and local government experience provides a clear advantage in name recognition and donor networks. Other candidates, including state Rep. Tram Nguyen and attorney John Beccia, have reported more modest fundraising totals and fewer high-visibility backers, leaving limited room for late surges ahead of the September 1 primary. Trader consensus reflects these structural edges in a race where established momentum typically proves decisive.