Minnesota Gov. Tim Walz, the Democratic vice-presidential nominee, has accelerated his preparations for his Oct. 1 debate against Sen. JD Vance (R-Ohio), participating in policy sessions and mock debates in his home state and on the road.

Walz’s team has enlisted Transportation Secretary Pete Buttigieg to play Vance in debate rehearsals, reprising his role from four years ago when he stood in for then-vice president Mike Pence during Kamala Harris’s practice sessions, according to multiple people familiar with the debate process who requested anonymity to describe confidential preparations.

Fueled by diet Mountain Dew and dressed in casual wear — cargo pants and a T-shirt — Walz was in a Minneapolis hotel on Wednesday, practicing with Buttigieg and taking notes on a yellow legal pad, the people said. The two have not yet held a full 90-minute mock debate, although they are expected to do so closer to Oct. 1, when Walz and Vance will meet in New York City for the debate hosted by CBS News.

Strategists for both parties say vice-presidential debates rarely affect the presidential race in a significant way. But with Harris and former president Donald Trump having held their one and likely only debate instead of three, and the undercard coming five weeks before Election Day, it may carry higher stakes.

“There are two key pivotal moments in a running mate’s time on the campaign: One is the convention speech and one is their debate performance,” said Matt Paul, who served as the campaign chief of staff to Sen. Tim Kaine (D-Va.) when he was Hillary Clinton’s running mate in 2016. “It seems this year, without a full presidential debate schedule and where this is falling in the race, it has somewhat raised the stakes of this debate.”

Walz, who often emphasizes his experience outside elected office on the campaign trail, has sought to tamp down expectations for his performance next month, following the timeworn tradition of trying to lower the bar for such events.

“Yes, I need to,” Walz said on MSNBC when asked if he had started thinking about his own debate shortly after the Sept. 10 Harris-Trump debate concluded. “Look, he’s Yale Law guy. I’m a public school teacher. So we know where he’s at on that.”

He added: “You will 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 will work hard. That’s what I do. I fully expect that Senator Vance, as a United States senator, a Yale Law guy, he will come well-prepared.”

For Walz, the debate will be the latest high-profile moment in his remarkable rise from a career as a public school teacher to becoming the Democratic Party’s vice-presidential nominee. It will also thrust him into the sort of traditional political setting that he has largely eschewed.

During his interview with Harris’s vetting team for the running mate slot, Walz told her aides he had never used a teleprompter. Walz’s folksy speaking style can resonate with audiences, and he has participated in debates when running for Congress and governor, but allies say debates may not be his strongest setting.

People familiar with Walz’s preparations say the governor, who was little-known nationally before Harris selected him in early August, sees the debate as an opportunity to continue to introduce himself to the nation and highlight Harris’s agenda. He and his aides view the debate as an extension of the campaign rallies and interviews he has participated in over the last month, and they expect him to focus not only on the contrast between Harris and Trump, but also between him and Vance.

Walz, who energized Democrats when he began referring to Republicans as “weird,” has leaned into his Midwestern roots and his experience as a football coach, part of an appeal to White, working-class voters in the “blue wall” states of Michigan, Wisconsin and Pennsylvania. He has ratcheted up attacks on Vance in recent weeks, slamming him for supporting Project 2025, a policy agenda compiled by the Heritage Foundation for the next Republican administration.

“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.

Vance has attracted an usual amount of attention since become Trump’s running mate, not all of it positive. He came under fire for previously calling Democrats like Harris “a bunch of childless cat ladies who are miserable.” In recent days, President Joe Biden and others have criticized him for embracing the falsehood that Haitian immigrants in Ohio are stealing and eating their neighbors’ pets.

At the same time, Walz will have to defend his own record against Vance, who has attacked the Minnesota governor for his handling of protests in Minneapolis after the murder of George Floyd, for ostensibly misleading the public about his military service, and for an array of liberal policy positions.

In contrast to Walz, who has only participated in a handful of interviews, Vance often appears on cable TV and has regularly taken questions from journalists, which allies view as effective practice for the debate.

A spokesperson for the Trump-Vance campaign declined to comment.

As soon as the Harris campaign selected a team to support her running mate — even before Walz himself was chosen — those aides started thinking about how to prepare for a vice-presidential debate. The team tapped Zayn Siddique, a lawyer at the firm Paul Weiss who worked in the Biden White House and helped both Biden and Harris prepare for debates, and Rob Friedlander, who recently departed the White House where he had worked on the National Economic Council, to oversee the debate prep.

The two have worked closely with Liz Allen, Walz’s campaign chief of staff, and Chris Schmitter, Walz’s chief of staff in the governor’s office and a senior adviser on the campaign.

A number of current and former Obama and Biden administration officials are also engaged in the preparations, including Kate Berner, a longtime Biden aide and a senior adviser to Walz’s team, who has been working with Buttigieg on playing Vance; and Michael Tyler, the Harris campaign communications director. Karen Dunn and Rohini Kosoglu, who co-led Harris’s debate preparations, have also consulted with Walz’s team on the preparations.

Buttigieg, who was among those vetted to serve as Harris’s running mate, is widely considered one of the Democratic Party’s best communicators, winning particular plaudits for sparring with hosts on Fox News. A White man from South Bend, Ind., Buttigieg is once again playing the role of a conservative Republican from the Midwest serving as Trump’s running mate.

Philippe Reines, who was initially cast as Vance when Harris was still Biden’s running mate, transitioned to play Trump in Harris’s presidential debate preparations. Harris’s performance against Trump was praised by Democrats and even some Republicans, as the vice president succeeded in getting under Trump’s skin as she needled him on his crowd sizes and legal troubles.

After the debate ended, Harris challenged Trump to another debate, and the former president wavered before declaring that since he had prevailed in the first matchup, he saw no reason for a second one.