Sen. Bernie Sanders is warning Maine Gov. Janet Mills to keep out of the state’s midterm Senate race, while backing Graham Platner, an oyster farmer and veteran who says on his website that he is aiming to flip the seat “for the working Mainers being priced out of our homes.”

“I have nothing against Janet Mills, but I think right now, Susan Collins is absolutely beatable,” Sanders told NOTUS. “She can be beaten, and I think it would be a really sad state of affairs to have to spend millions of dollars on a divisive primary. We should be focusing on beating Susan Collins, and Platner can do that.”

His comment followed an earlier tweet in the day where he boosted Platner over Collins.

“Graham Platner is a great working class candidate for Senate in Maine who will defeat Susan Collins,” Sanders wrote on X Thursday.

Sanders, an independent from Vermont who caucuses with Democrats, said he is endorsing Platner for the Democratic ticket because he is a “working-class guy.” Sanders’ endorsement is sure to boost Platner’s candidacy, providing legitimacy to the populist political newcomer.

“He’s running a great campaign. He’s drawing large crowds. He’s raising money. There is an enormous enthusiasm for him in Maine, and I think he is touching on exactly the right issues,” Sanders told NOTUS. “I was there with him, as you may recall, last month, at a huge rally. I think 7,000 people came out. He’s a great candidate, and I think that he has a great chance to win.”

Mills, a Democrat, has served as Maine governor since 2019 and has long been the target of speculation over a potential run for Senate. Sources familiar with Mills’ thinking suggested to NOTUS earlier this year that she is keeping the door open to a run that could launch as late as the end of 2025.

“If there comes a time, she might decide to do all kinds of things,” the source said. “And running for Senate might be one of them.”

Platner has made attacks on Collins, the Republican incumbent, central to his message. In the meantime, he has grown his popularity, raising over $3 million since launching his campaign this summer.

In a post on X earlier this year, Platner said, “I’m running for US Senate to defeat Susan Collins and topple the oligarchy that’s destroying our country.”

In a separate post, he said, “Over the years Susan Collins has made it crystal clear that she does not care how many people lose access to healthcare, and this week she shut down the government instead of voting to let Mainers get the care they need. It’s despicable.”

Some Democratic leaders, such as Senate Minority Leader Chuck Schumer, have been encouraging Mills, who has termed out as Maine’s governor, to run for Senate.

Sanders, however, pushed back on his colleagues’ endorsement, calling the push for a competitive primary that could divide the party “disappointing.”

“We need to focus on winning that seat & not waste millions on an unnecessary & divisive primary,” he said in the X post.

Sanders’ comments came after Axios reported that Mills is planning to announce her campaign for Senate any day now.

New Mexico Senator Martin Heinrich has also spoken out in support of Platner, posting, “We need more candidates like this.”

Two other Democratic candidates, Maine Beer Company owner Dan Kleban and former congressional aide Jordan Wood, are also in the race for the Senate seat.

This story was produced as part of a partnership between NOTUS, a publication from the nonprofit, nonpartisan Allbritton Journalism Institute and The Maine Monitor, a nonpartisan, nonprofit news organization covering the state of Maine.