Dan Koh leads the MA-06 Democratic primary field as the consensus frontrunner, driven by his substantial fundraising edge exceeding $3.5 million through March 2026 and broad endorsements from unions and Democratic groups in the open-seat contest following Seth Moulton's Senate bid. State Rep. Tram Nguyen trails in market pricing despite an internal poll showing her at 28% support among likely primary voters in late May, ahead of Koh at 18% with 24% undecided, reflecting her local legislative profile but more limited resources. The September 1 primary features a crowded field where recent internal surveys indicate persistent undecided voters and shifting dynamics among contenders like John Beccia, with withdrawals including Rick Jakious further consolidating attention on the top tier ahead of the vote.