Graham Platner may have overwhelmingly won the Maine Democratic Senate primary Tuesday night, but some Senate Democrats remain on the fence about supporting him.

Platner, who overcame numerous controversies to finish with 72% of the vote, will challenge Sen. Susan Collins, R-Maine, who has represented the state since 1996.

Sen. Mark Kelly, D-Ariz., declined to endorse Platner, even though he said he believes he could defeat Collins.

"The path for us winning back control of the Senate runs through Maine," Kelly said to Politico.

But Kelly said Platner has "got things to explain."

In recent months, Platner has faced scrutiny over past online posts, sexting with other women after marrying his wife, allegations from former partners and criticism over a tattoo that resembles a Nazi symbol.

Platner has disputed or pushed back on aspects of the allegations and has sought to reassure voters that he has changed from earlier periods of his life.

"I'm not proud of who I was then, but I am proud of the work I've done since, and the movement we are building in Maine," Platner told the Portland Press Herald in response to reporting about his past.

Sens. Catherine Cortez Masto, D-Nev., who endorsed Gov. Janet Mills in the primary, and Tammy Duckworth, D-Ill., also declined to endorse Platner when asked by Politico.

Sen. Peter Welch, D-Vt., said he supports Platner, but added he still has "work to do."

"The challenge that Platner has is the challenge that any candidate has, and it's to address in a direct way both personal and political issues that are legitimate questions for the voters. He's got to do that," Welch said to Politico.

"Until the election is over, he's got work to do, every day in every way," Welch added.

Collins is the only Republican senator seeking reelection in a state Vice President Kamala Harris won in 2024 and the state is considered essential if Democrats are to flip four seats and regain the upper chamber.

Sen. Bernie Sanders, I-Vt., was an early backer of Platner, while Democratic Sens. Ruben Gallego, Ariz., Brian Schatz, Hawaii, and Elizabeth Warren, Mass., have endorsed Platner.

"Platner won a landslide victory last night, and I am quite confident that Democrats who want to regain the Senate will be supporting him as the Democratic nominee," Sanders said.

Sen. Mazie Hirono, D-Hawaii, said she was ready to endorse Platner, noting he apologized for his past mistakes.

"That says a lot in contrast to the president, who never admits doing anything that is untoward, and who just blames everybody else, and who prosecutes people," Hirono said to Politico. "I think Maine voters have expressed themselves and they're willing to give him a chance."

Sen. Elissa Slotkin, D-Mich., who was critical of Platner following allegations of forcefully grabbing an ex-girlfriend, said she plans to "work with whoever the Mainers elect, period."

"The way that this president has completely railroaded my Republican colleagues in this body, they don't deserve to run a separate branch of government," Slotkin said to Politico. "And if we want any chance of putting a check and balance on him that involves electing Platner."

"I just hope I'm not caught again live on TV answering the same questions about bad behavior," Slotkin added.