The open Massachusetts 6th Congressional District Democratic primary, vacated by Rep. Seth Moulton for his U.S. Senate bid against Sen. Ed Markey, sees former Biden aide Dan Koh commanding trader consensus at 74% implied probability, propelled by superior fundraising exceeding $2 million without PACs, endorsements from Kamala Harris, Marty Walsh, Pete Buttigieg, and recent labor unions like Merrimack Valley Building Trades, plus first-to-qualify ballot access on March 27 with over 2,000 signatures across all 39 district towns. Moulton's 12% share stems from incumbency name recognition despite his withdrawal, while state Rep. Tram Nguyen, ex-Rep. Jamie Zahlaway Belsito, and others trail amid early March forums debating health care, immigration, and foreign policy. No public polls exist; the May state convention and September 1 primary loom as pivotal.