Since Collins is such a unique candidate in the state, I will primarily focus on the 2026 Democratic primary as well as her previous Senate election in 2020.
Because so few prior elections have taken place, there is not as much useful information from previous election cycles. Here are the key takeaways:
Maine is a blue state. Maine has consistently voted for Democrats in the last 9 Presidential cycles, which—in today's more politically polarized environment—may prove beneficial to Troy Jackson.
Collins has beaten the odds. Susan Collins outperformed polling by a significant margin in 2020, and has consistently won re-election in a deeply Democratic state. This calls Jackson's polling into question and gives Collins very good odds to win once more in November.
Jackson's last-minute entry into the race will harm him. Jackson, a relative newcomer in statewide Maine politics, will have to face an electoral juggernaut who has represented Maine for nearly three decades (she first won in 1996).
The 2026 Democratic primary initially pitted political newcomer Graham Platner, who ran as a progressive, against Maine Governor Janet Mills—a moderate endorsed by establishment figures like Chuck Schumer. As the primary came closer, Graham Platner began to crush Mills in polling, eventually leading Mills to drop out of the race.
While the establishment reluctantly began to coalesce around Graham Platner, he was later forced to withdraw after being credibly accused of rape, and was eventually replaced by Troy Jackson. Troy Jackson, while also a progressive candidate, has had significantly less time to introduce himself to Maine as the Senate candidate, and the sudden replacement echoes Kamala Harris' last-minute campaign for President after Democratic candidate Joe Biden ended his campaign. It remains to be seen how dramatically this will affect Jackson's odds in November.
Polling often gets elections wrong; it is extremely difficult to predict voter turnout or voting behavior in elections. In Maine, this will prove even more difficult: Susan Collins' unique success as a Republican in a Democratic state makes other races far less insightful about her chances. Furthermore, the other Senator for Maine, Angus King, runs as an Independent, leading to an entirely different political process.
As a result, the most helpful recent data point for Maine is the 2020 Senate race between Susan Collins and Democratic candidate Sara Gideon. In 2020, based on a polling average from 270toWin, Susan Collins was expected to lose her race by nearly 4 points. Instead, she won by a 9-point margin.
This margin is slightly skewed—had ranked-choice voting applied, she would have won by a less sizeable four points due to Independent candidate Lisa Savage openly campaigning as a Democrat whose voters should back Gideon. However, even a 4-point victory for Susan Collins shows a dramatic overperformance compared to polling, meaning no polling lead is truly safe for Troy Jackson.
The Presidential election also showcases Collins' strength: in 2020, Biden defeated Trump by a safe margin, winning 53% of the vote to Trump's 44%. Susan Collins' history of overperformance may prove decisive in this election cycle.