Dan Koh's 79.5% implied probability as the trader consensus frontrunner in the open Massachusetts 6th Congressional District Democratic primary stems from his strong positioning to succeed Seth Moulton, who shifted to a U.S. Senate challenge against Ed Markey. Former President Biden's endorsement on May 4 elevated Koh's national profile as a Biden administration alum, alongside earlier backing from Pete Buttigieg and local figures like Swampscott Select Board Chair Katie Phelan. Koh leads the sole credible poll and boasts superior fundraising compared to challengers like Rachel Creemers and Tram Nguyen, in a crowded field narrowed by Rick Jakious's April dropout. With the September 1 primary approaching, his momentum reflects skin-in-the-game assessments of voter turnout and endorsements in this safely Democratic district.