The closely matched probabilities across turnout brackets in the 2026 Massachusetts U.S. Senate election reflect uncertainty in a low-competition general election in a solidly Democratic state. Incumbent Ed Markey holds a clear lead in recent Democratic primary polling over challenger Seth Moulton ahead of the September 1 primary, which could shape base mobilization efforts. Historical turnout in similar safe-seat Senate races tends to lag presidential-year levels, with participation driven more by local enthusiasm, early and absentee voting patterns, and any spillover from national midterm dynamics than by the outcome itself. Developments such as shifts in primary polling margins, candidate debate performance, or changes in voter registration and get-out-the-vote spending could widen separation among the ranges before November 3.