As Sen. JD Vance prepares to face Gov. Tim Walz in next week’s vice-presidential debate, the Ohio senator is turning to Minnesota Rep. Tom Emmer to help him in debate rehearsals by playing Walz, sources familiar with the plans told ABC News.

One of the sources said Emmer was invited to stand in for Walz so that Vance could prepare to take on the governor’s folksy personality.

Vance’s debate preparations have included sessions at his Cincinnati home and online sessions with his team and with Jason Miller, a senior advisor on former President Donald Trump’s campaign, a source told ABC News.

Vance has spent the last month reviewing debate plans, strategies and potential questions, according to a source familiar with the senator’s debate preparations.

Vance is expected to paint Walz as too liberal, focusing on the policies he has passed while governor of Minnesota, one of the sources said.

Emmer is the third-ranking Republican in the House and serves as the majority whip. Emmer also previously served as the chair of the National Republican Congressional Committee.

Emmer backed Trump for president earlier this year — despite the fact that the former president called Emmer a “Globalist RINO” who is “totally out-of-touch” with Republican voters, effectively tanking Emmer’s speakership bid in October 2023.

Walz and Emmer overlapped in the House from 2015 through 2019 before Walz ran for governor of Minnesota.

Vance’s wife, Usha Vance, a Yale law school graduate and who clerked for U.S. Supreme Court Chief Justice John Roberts, has also been involved in the debate preparation sessions, a source told ABC News.

Those helping Vance prepare have been immersed in learning Walz’s debate style by watching videos of his past debates from his previous campaign runs, according to the source.

The source also points to Vance’s frequent media interview as helping him prep for the debate, specifically citing his frequent appearances on the Sunday shows and engaging with “contentious network hosts.”

Walz’s debate preparations are also underway with Transportation Secretary Pete Buttigieg acting as a Vance stand-in during the Walz team’s debate rehearsals. Walz has also held policy sessions with his own longtime aides, Biden White House alumni and members of the Harris-Walz campaign team.

The vice presidential debate hosted by CBS News is set to be in New York City on Tuesday, Oct. 1, 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.

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A growing effort backed by Republicans, including former President Donald Trump, to switch Nebraska’s electoral process to winner-take-all hit a major snag on Monday after a key state lawmaker said he wouldn’t support such a change before the November election.

State Sen. Mike McDonnell, one of the key Republicans holdouts GOP Gov. Jim Pillen was looking to for support to break a likely filibuster, said in a statement that he would not vote to change electoral process before then.

Instead, McDonnell said he believed the legislature should take up the issue in next year’s legislative session, which tentatively starts the first week of January 2025.

“In recent weeks, a conversation around whether to change how we allocate our electoral college votes has returned to the forefront,” McDonnell said. “I respect the desire of some of my colleagues to have this discussion, and I have taken time to listen carefully to Nebraskans and national leaders on both sides of the issue. After deep consideration, it is clear to me that right now, 43 days from Election Day, is not the moment to make this change.”

“I have notified Governor Pillen that I will not change my long-held position and will oppose any attempted changes to our electoral college system before the 2024 election,” he added. “I also encouraged him and will encourage my colleagues in the Unicameral to pass a constitutional amendment during next year’s session, so that the people of Nebraska can once and for all decide this issue the way it should be decided — on the ballot.”

Pillen released a statement last week saying he would not call a special session unless Republican legislators could show they have 33 votes needed to break an expected Democratic filibuster. U.S. Sen. Lindsey Graham, a South Carolina Republican and staunch ally of Trump, traveled to Nebraska last week to lobby lawmakers and met with stakeholders.

ABC News spoke to Nebraska Rep. Mike Flood, who agreed that McDonnell was a key holdout and understood the Nebraska legislature needed at least three more votes to break a very likely filibuster.

If the other state Senate holdouts stand firm, McDonnell’s decision effectively throws cold water on the ongoing effort to switch the state’s Electoral College vote to winner-take-all, even after Republican members of Congress and Trump pushed for the change.

Flood, a Republican who represents Nebraska’s 1st Congressional District, said Trump engaging directly on the issue “underscores how big of a deal this is.” Flood, who supports changing the process along with the rest of Nebraska’s federal delegation, said Nebraska “has the right to speak with the majority of its citizens, by and through its legislature, and that’s what I want to see done.”

The winner-take-all electoral change would be pivotal if the Republican-leaning state allocates all of its five electoral votes solely to Trump, instead of dividing them with Vice President Kamala Harris.

Nebraska split its electoral votes in 2020, with President Joe Biden flipping the 2nd district, which includes Omaha. Without gaining the votes from Nebraska’s 2nd district, Harris could not win the general election with “blue wall” of Wisconsin, Michigan and Pennsylvania alone. It would also create a new possibility for a 269-269 Electoral College tie.

“It is amazing to think that could come down to Nebraska, but I think the math and the reality is that it very well may be true,” Flood said.

Late Monday afternoon, Trump thanked Pillen for attempting to “simplify the complexity” of the state’s electoral map, while attacking state McDonnell for opposing it, calling him a “Grandstander.”

“I would like to thank Governor Jim Pillen of Nebraska for trying to help the Republican Party simplify the complexity of the State’s Electoral Map,” Trump wrote on his social media.

“It would have been better, and far less expensive, for everyone! Unfortunately, a Democrat turned Republican(?) State Senator named Mike McDonnell decided, for no reason whatsoever, to get in the way of a great Republican, common sense, victory. Just another ‘Grandstander!’” Trump wrote.