Incumbent Sen. Ed Markey holds an 82% implied probability in the September 1, 2026 Massachusetts Democratic Senate primary due to his long-standing statewide recognition, consistent polling leads over challenger Rep. Seth Moulton, and endorsements from key figures including Rep. Ayanna Pressley. Moulton, at 19%, has gained some ground through debates and fundraising while criticizing Markey’s age and pushing generational turnover plus congressional age limits, with a recent endorsement from New Jersey Gov.-elect Mikie Sherrill. Polls from mid-2026 showed Markey’s advantage narrowing at times amid undecided voters, yet his position as the sitting senator has sustained stronger trader consensus. Minor candidates Pressley and Alexander Rikleen register negligible support given their limited or absent campaigns. The race remains shaped by primary timing and voter preferences in a heavily Democratic state.