Dan Koh leads trader consensus at 65% implied probability in the crowded MA-06 Democratic primary for the open seat vacated by Seth Moulton, who is challenging Sen. Ed Markey, due to his dominant grassroots fundraising via ActBlue—reportedly topping the field as of late March—and high-profile endorsements including Transportation Secretary Pete Buttigieg, former Boston Mayor Marty Walsh, ex-Rep. John Tierney, and the Massachusetts Nurses Association. These factors signal strong establishment and labor support in a district spanning suburban North Shore communities, positioning Koh as the frontrunner five months before the September 1 primary. Trailing contenders like Kevin Larivee, a state health executive official, and veterinarian Mariah Lancaster draw secondary odds from local ties and progressive appeals, but lack comparable resources amid fragmented field dynamics; filing deadline looms August 25.