Susan Collins

Democrats hoping to flip a U.S. Senate seat in Maine are facing growing questions about their presumptive nominee, Graham Platner, as a sexting scandal and past controversies threaten to overshadow his challenge to five-term Republican Sen. Susan Collins.

Platner, who has gone from underdog to favorite in the race, acknowledged exchanging sexually explicit text messages with other women while married to his wife, Amy Gertner. Asked about Platner’s assertion that the messages should be private, Collins said, “I think it’s a reflection of character.”

Gertner defended her husband on Saturday.

“Graham and I have a great marriage. Being married is hard. Being newly married is hard. Being newly married and going through infertility is hard. Being newly married, going through infertility and a Senate campaign is hard," she said during a video released by Platner's campaign.

Platner has also apologized for offensive posts on Reddit, including calling himself a communist and criticizing police. He has had a tattoo covered up that he got while in the Marines that resembled a Nazi symbol.

Platner was in Washington, D.C., on Tuesday, meeting with Democratic senators amid concerns that he could become a drag on the party. Sen. Cory Booker, D-N.J., said over the weekend that there are questions Platner needs to answer.

“Yeah, I have concerns. That guy has questions to answer and that’s what campaigns are for," he told ABC News.

Senate Democratic leader Chuck Schumer was asked multiple times about Platner’s campaign going forward.

“I met with Graham Platner today. We’re going to beat Susan Collins and take back the Senate," Schumer said. He repeated the line "We’re going to beat Susan Collins and take back the Senate," multiple times.

Sen. Bernie Sanders, I-Vermont, said he is standing by the progressive candidate.

“Why do the richest people in this country want to defeat Graham Platner? That should tell you everything you need to know because he stands up for working people. Is he a saint? I guess not. I don’t know too many saints here," he said.

Maine’s primary is next week. Platner’s opponent, former Gov. Janet Mills, has recently said she is still on the ballot despite suspending her campaign a month ago.