Incumbent Republican Sen. Susan Collins, first elected in 1996, is seeking a sixth term in 2026. Maine is the only Republican-held Senate seat up for election in 2026 in a state carried by Kamala Harris. Collins remains the lone Republican representing a New England state at the federal level and has consistently outperformed other GOP candidates in Maine. In 2020, she won re-election by about eight points despite widespread predictions of defeat, even as Joe Biden carried the state by nine points. With ticket-splitting declining and a midterm election under a Republican presidency, Collins is widely regarded as the most vulnerable incumbent Republican senator this cycle. Notably, Collins enters the race with her lowest personal approval ratings of her career.

Maine, a largely rural New England state with a moderate and independent-leaning electorate, has voted Democratic in every presidential election since 1992. In 2024, Kamala Harris carried the state by 7 points—a slightly narrower margin than Biden’s 9-point win in 2020—marking one of the most muted partisan shifts in the nation. The state’s Class II Senate seat has been held by Republicans since 1979. On the Democratic side, Governor Janet Mills and Sullivan Harbor Master Graham Platner are the leading contenders; Mills is backed by national party leaders, while Platner showcased fundraising prowess and has drawn progressive support despite early controversy surrounding his campaign.