Graham Platner, a United States Army veteran and oyster farmer, has won the Maine Democratic primary for the Senate, setting up a high-stakes race against Republican Senator Susan Collins.

Platner’s victory on Tuesday came after days of questions over damaging revelations about his past personal conduct, particularly in his relationships with women.

Platner, in his acceptance speech, acknowledged voters’ concerns, pledging to earn their “trust, faith and support” over the course of the campaign.

Democrats see the race as a top opportunity to flip a Republican-held seat and a must-win as the party tries to claim control of the Senate in November.

Collins, first elected in 1996 and chair of the powerful Committee on Appropriations, is the last Republican senator from New England. Maine backed Democrat Kamala Harris over Donald Trump in the 2024 presidential race.

Platner, 41, has focused his campaign on the rising cost of living, housing affordability and healthcare, and secured early endorsements from progressive figures, including Senator Bernie Sanders. But Governor Janet Mills, who withdrew from the race citing fundraising difficulties, has yet to endorse him.

Controversies shadow Platner’s campaign

His candidacy has been clouded by a series of controversies, including reports of sexually explicit messages exchanged with women while he was married and allegations from a former girlfriend of physical intimidation.

Platner’s campaign has disputed the claims.

Old online posts also surfaced in which he appeared to endorse political violence and make remarks dismissive of military sexual assault, comments he attributed to a period of acute mental health struggles, including PTSD and depression following two combat deployments.

He also apologised for posts containing homophobic slurs and insults directed at rural communities and law enforcement.

A tattoo later identified as a Nazi symbol prompted further scrutiny. Platner, who has since had it covered, maintained he was unaware of its significance.

In his victory speech, Platner stressed a message of redemption as he promised to oust Collins. “If you believe, as I do, that we can change our politics and change our country, then you must also believe that people can change,” he told supporters in Blue Hill, the rural town where he was born.

“And the reason I believe that is because I have lived it.”

He also slammed Collins, accusing her of rubber-stamping conservative Supreme Court justices and supporting what he called “endless wars”. A Marine and Army veteran who served in two conflicts, Platner addressed Collins, saying, “You and your friends profited, and my friends died.”

Collins, who was unopposed in the Republican Maine primary, has countered that her experience and key position as chair of the Committee on Appropriations are two reasons to send her back to the Senate.

“While others talk about revolution and division, Susan Collins is delivering for Maine communities by funding rural hospitals, supporting our shipbuilders and fishermen, improving infrastructure, expanding broadband, and strengthening public safety,” said Collins’ spokesperson, Shawn Roderick.

“Maine people are practical. They care about whether their communities are stronger and their families are better off. That’s exactly what Susan Collins is focused on every single day.”

Elsewhere in Maine, ranked-choice tabulations will be required to determine the outcomes of the Democratic gubernatorial primary and the 2nd Congressional District race, where no candidate secured an outright majority. The eventual Democratic nominee in the district will face former Governor Paul LePage, a close ally of Trump.