In the open Massachusetts 6th Congressional District Democratic primary—vacated by Seth Moulton's Senate challenge to Ed Markey—traders price Dan Koh as overwhelming frontrunner at 71.5% implied probability, propelled by his fundraising dominance, exceeding $2 million raised including a recent first-quarter surge, and endorsements from Kamala Harris, Pete Buttigieg, Marty Walsh, Jennifer Granholm, and local leaders like Swampscott Select Board Vice Chair Doug Thompson. Mariah Lancaster follows at 9.3% after her January entry and forum performances, in a fragmented field of over 10 candidates. Early April fundraising disclosures and March forums on healthcare, immigration, and foreign policy underscore Koh's establishment momentum, with no public polls yet; the September 1 primary looms as the resolution date.