Walz debate prep underway with Pete Buttigieg as Vance stand-in

Minnesota Gov. Tim Walz's preparation for the Oct. 1 vice presidential debate with Sen. JD Vance is well underway, sources familiar with the process have confirmed to ABC News.

He's already held some mock debates, sources said, with Transportation Secretary Pete Buttigieg, in his personal capacity, acting as a Vance stand-in, and held policy sessions with his own longtime aides, Biden White House alumni and members of the Harris-Walz campaign team.

Buttigieg was in Minneapolis as recently as Wednesday to help him prepare. Walz has also been practicing on the road as he campaigns.

Biden White House alumni Rob Friedlander and Zayn Siddique are running the preparations. Siddique, who is currently an attorney at the firm Paul Weiss and served as senior adviser to Bruce Reed, the White House deputy chief of staff under President Joe Biden, has also been part of the vice president's debate preparations.

Friedlander was chief of staff for the White House National Economic Council and senior adviser for communications.

Friedlander and Siddique are being supported by a larger team that includes Liz Allen, a veteran political operative who stepped down from her role as head the State Department's public diplomacy office in August to become chief of staff on Harris' running mate team. Chris Schmitter, Walz's longtime aide who led his gubernatorial races and debate, is also helping along with Harris-Walz communications director Michael Tyler, sources say.

The vice presidential debate hosted by CBS News is set to be in New York City, the network has announced, with both Walz and Vance agreeing to participate. The debate will be moderated by "CBS Evening News" anchor and managing editor Norah O'Donnell and "Face the Nation" moderator and CBS News chief foreign affairs correspondent Margaret Brennan.

The sources stress that the vice presidential debate won't be the "end all be all" for Walz, who has acknowledged himself that he's "working hard" to "try and learn the issues" but is up against Vance, who "as a United States senator, a Yale Law guy" will come prepared.

"You'll hear me talk like I have about things that impact Americans, making sure they have the opportunity to thrive, making sure that we're being factual in how we talk about that. And so I'm looking forward to it. I'll work hard. That's what I do," Walz said about the VP debate on MSNBC in the aftermath of the presidential debate between Harris and former President Donald Trump. "I fully expect that Senator Vance, as a United States Senator, a Yale Law guy, he'll come well prepared."

"Debates and VP Debates don't matter all that much in polling - this will be one of many data points for voters," sources said about the significance of the debate, also stressing that "Vance is a skilled debater."

The campaign sees the debate as one of "many" opportunities for Walz to present Harris' agenda to Americans. He'll also use the debate to introduce himself and highlight the Democratic ticket's vision for the future.

"This debate will serve as another clear opportunity for Governor Walz to present Vice President Harris' winning vision of a New Way Forward to the American people who are ready to turn the page on Donald Trump," Emily Soong, a spokesperson for the Harris-Walz campaign said in a statement to ABC News.

Vance's team has not commented to ABC News on how he's preparing for the debate. The Washington Post was first to report the details of Walz's preparations.

ABC News' Hannah Demissie contributed to this report.