On the campaign trail, Democratic presidential primary contender Bernie Sanders may talk about unifying the party to defeat President Trump this fall, but a former governor of his home state of Vermont argues that at the end of the day, Sanders is out for himself.

Peter Shumlin, who served as Vermont’s Democratic governor between 2011 and 2017, said that Sanders and his campaign team are not above playing “dirty” and that the independent, self-described democratic socialist senator has no real loyalty to the Democratic Party.

“What I’ve seen in Bernie’s politics is he and his team feel they’re holier than the rest. In the end, they will play dirty because they think that they pass a purity test that Republicans and most Democrats don’t pass,” Shumlin said in an interview with Politico.

“What you’re seeing now is, in the end, even if he considers you a friend, like Elizabeth Warren, Bernie will come first," Shumlin added. "That’s the pattern we’ve seen over the years in Vermont, and that’s what we are seeing now nationally.”

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The comments by Shumlin, who has endorsed former Vice President Joe Biden for the Democratic presidential nomination, mark the latest blowback Sanders faces amid his dispute with fellow senator and Democratic hopeful Elizabeth Warren of Massachusetts.

While the two progressive lawmakers had generally shied away from attacking each other and their policy proposals while campaigning, the armistice disintegrated during Tuesday’s debate when a hot mic caught Warren asking Sanders if he called her a liar on national television, this after Sanders publically denied ever telling her that a woman could not be elected president.

Cracks in the détente between Sanders and Warren began to appear before reports broke of Sanders' alleged comments to Warren during a private meeting two years ago.

In a story that broke last weekend, Sanders’ campaign put out a series of talking points aimed at painting Warren as a candidate attracting “highly-educated, more affluent people who are going to show up and vote Democratic no matter what.”

The script added: “She's bringing no new bases into the Democratic Party.”

Shumlin criticized Sanders for the talking points and compared his campaign’s strategy to the one the Vermont senator employed during his bid for the Democratic nomination in 2016. He said that Sanders is trying to “Hillarize” Warren by portraying her as the candidate for the wealthy, referring to Hillary Clinton.

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“We should be weakening Donald Trump, not each other,” Shumlin said. “I’m concerned that we’re seeing a replay of the kind of dynamics that didn’t allow Hillary to win.”

Shumlin isn’t the only Democrat concerned about the ongoing feud between Sanders and Warren ultimately playing to the advantage of their political rivals.

Warren's and Sanders' aides have for days attempted to de-escalate the feud as some progressives worry that ill will between the cause's two leading voices will ultimately hurt both of them and could benefit more moderate Democratic presidential hopefuls such as Biden and Pete Buttigieg, former mayor of South Bend, Ind.

The Associated Press contributed to this report.