Dan Koh holds a commanding lead in the Massachusetts 6th Congressional District Democratic primary, with trader consensus reflecting his substantial fundraising advantage, early polling edge, and recent high-profile support. The open seat created by Representative Seth Moulton’s Senate bid has drawn a crowded field, yet Koh has outpaced rivals in campaign contributions exceeding $3.5 million, grassroots organizing across every town in the district, and ballot qualification. Former President Biden’s endorsement on May 4 added momentum, joining other recent backers including End Citizens United and local officials. Other candidates such as Tram Nguyen and John Beccia have reported more modest hauls, while no challenger has consolidated enough backing to close the gap ahead of the September 1 primary.