Some Democratic allies of Gov. Tim Walz are concerned about how he will fare in the vice presidential debate between him and Sen. JD Vance, worrying that the Minnesota governor remains untested.

"We’ve never seen him on the national scale before," a Minnesota Democrat told Politico. The outlet reported that Vance hasn't been tested in a scenario like a debate, where he will face direct questioning and attacks from the other side. 

Walz and Vance are set to clash on Tuesday during the first vice presidential debate, which will be moderated by CBS News' Norah O'Donnell and Margaret Brennan. 

"He can be very: ‘That’s it I’m done,’" a Minnesota state lawmaker told the outlet. Politico reported that Walz shuts down conversations and gets defensive when he's asked to discuss "missteps" in private, and it noted Walz was "still largely untested and has never faced the intense, direct questioning that Vance is sure to launch."

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Gov. Tim Walz delivers the keynote address at the Human Rights Campaign's national dinner in Washington, D.C., Sept., 7, 2024. (Dominic Gwinn/Middle East Images/AFP via Getty Images)

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"She did so strong. She’s actually made it very difficult for Walz, because I don’t see any way that he could match her level of intensity and humor," another ally of the Minnesota governor said, noting Vice President Kamala Harris' debate performance against former President Trump that received high media praise.

Harris' inner circle reportedly discussed Walz's habit of being "gruff and brass," Politico reported, while they were vetting him. 

According to the outlet, a Minnesota lawmaker recalled Walz saying "'Alright, I’ve done all the answering I’m going to do. Meeting’s over,’" when he was asked about questions he didn't want to talk about. 

A Democratic lawmaker described a call with Walz in 2020 amid the George Floyd riots, during which Walz reportedly "signaled he was done with the conversation," after he was pressed on why he didn't call the National Guard in sooner. 

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Republican vice presidential nominee Sen. JD Vance speaks during a campaign rally Saturday, Sept. 28, 2024, in Newtown, Pennsylvania. (AP Photo/Laurence Kesterson)

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"I don’t think he hung up, but definitely that was it. The call was over," the Democratic lawmaker said.

"At times, he could be the exact opposite of what he usually is. That was one of them," the person told Politico.

Politico also reported that Walz struggled to explain Harris' economic agenda and kept repeating the words "opportunity economy." The report said it came off as vague to those in attendance. 

MSNBC's Claire McCaskill, a former Democratic senator, said during an interview on Monday that expectations for the VP debates should be "lowered."

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"I’m just a little worried about the expectations game at this point. I think people — yes, J.D. Vance has said some really, I think, disqualifying things about women and how he views people and their role in life. But he will be articulate and he will be prepared and he will be better than Trump was," she said. 

McCaskill said it would be a "challenge" for Walz to be able to counter Vance and "stay really likable and relatable."

"I just think we need to lower expectations a little bit, because then we can all be pleasantly surprised if I’m wrong and that Tim Walz just mops the floor with him the same way Kamala Harris mopped the floor with Donald Trump," McCaskill added.

Fox News Digital has reached out to the Biden-Harris campaign for comment.