Newsweek has reached out to Platner, Mills, and Collins' campaigns for comment via email on Tuesday.
Democrats are hoping to topple Collins, a five-term incumbent who has been popular in Maine despite its Democratic lean. Maine is likely a must-win for Democrats if they hope to wrest control of the upper chamber while facing a challenging Senate map. The race has been labeled as a "toss-up" by the Cook Political Report.
The Democratic primary race between Governor Janet Mills and Platner has divided the party. Some believe Mills, who has won statewide by comfortable margins in both her 2018 and 2022 gubernatorial bids, would be the strongest candidate to take on Collins. Others, however, believe Platner is a candidate who represents a new generation of leadership and would be a stronger contrast against Collins in November.
In Maine, unenrolled voters, those not registered with a political party, may participate in primary elections, though they may vote in only one party's primary.
A University of New Hampshire Survey Center Pine Tree State poll released Tuesday found that in a hypothetical Senate matchup, Platner would receive 49 percent of the vote to Collins' 38 percent, with 4 percent undecided. Among registered unenrolled voters, Platner and Collins share a similar level of support, Collins with 45 percent and Platner with 44 percent. A higher share of independents back Platner in the hypothetical matchup, 47 percent to 38 percent for Collins.
The Democratic advantage narrows if Mills is the nominee, with Mills at 41 percent and Collins at 40 percent. Nine percent of voters remain undecided.
The wider poll of the general election match-up included 1,105 voters. The poll of 478 likely primary voters was conducted between February 12 and February 16 and has a margin of error of plus or minus 4.5 percentage points.
When asked specifically about the Democratic primary, participants favored Platner over Mills as the nominee, 64 percent to 26 percent. Mills support has largely stayed the same compared to a similar poll in October 2025, which found 24 percent backing her as their Democratic primary choice, while 58 percent said Platner.
In terms of favorability, 71 percent of the poll's participants view Platner favorably, while 51 percent view Mills as such.
Previous polls also showed Platner ahead of Mills, including a Z to A Research survey last year, which showed Platner with a double-digit lead over Mills in the Democratic primary. Fifty-eight percent of respondents said they would vote for Platner, while 38 percent said they were supporting Mills. It surveyed 1,482 likely midterm voters from November 14 to November 18.
Graham Platner shared the poll results in an X post on February 19: "I won't stand by and watch Maine get ripped apart. I'm with working Mainers, not the billionaires and corporations."
Governor Janet Mills said in an X post on February 21: "A year ago, I stood up to Trump more in one day than @SenSusanCollins has in nearly 30 years."
Senator Susan Collins said in a February 10 X post: "As a proud native of Maine, I've dedicated my life to serving our state and nation. I am deeply grateful for the unwavering support Mainers have shown me over the years. It is an honor to serve you and I'm excited to announce my run for re-election to the U.S. Senate in 2026."
Maine's primary is set to take place on June 9, 2026. Governor Mills has agreed to several debates ahead of the June primary, according to Maine Moring Star.
Democrats need to flip four seats in November to take back the majority in the Senate. Maine is one of the strongest targets as it has backed the Democrats in every presidential race since 1992.