NEW YORK - With a second face-to-face showdown between Vice President Kamala Harris and former President Trump unlikely - and with a margin-of-error race with five weeks until Election Day in November - there's a lot on the line in the vice presidential debate.
While debates between the running mates are the undercard of a White House race and have rarely moved the need much in the past, when Republican vice presidential nominee Sen. JD Vance of Ohio and Minnesota Gov. Tim Walz, the Democrats' nominee, face-off on Tuesday, there will be heightened stakes.
Any major knockout blow - or agonizing misstep - could turn what's traditionally seen as a second-tier event into an impactful showdown.
"Given that we're only likely to have one head-to-head matchup between the principal candidates and this is the last meet up between the two tickets directly before the election, it heightens the importance and significance of this debate," longtime Republican strategist and communicator Ryan Williams, a veteran of multiple presidential campaigns, told Fox News.
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Most political pundits said that Harris bested Trump last month in their first and likely only debate. And flash polls of debate watchers agreed.
So a strong showing by Vance in Tuesday's vice presidential debate could give Trump a boost.
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And there's a precedent from twelve years ago.
After a shaky first debate by then-President Barack Obama against 2012 GOP presidential nominee Mitt Romney, then-Vice President Joe Biden's well-regarded performance in the running mate debate against Romney running mate Rep. Paul Ryan gave the Democrats' ticket a big boost.
Heading into the 2024 vice presidential debate, the 40-year-old Vance has been very talkative, sitting for scores of interviews and taking plenty of questions from reporters on the campaign trail.
Walz, who is 60, has been much more reluctant to speak with the national news media.
The governor has been in debate camp ahead of the showdown, to prepare. Walz huddled with advisers and Transportation Secretary Pete Buttigieg - who played the role of Vance in mock debates - in Harbor Springs, Michigan, near the northern tip of the state's lower peninsula.
Also helping out - Walz's wife - Minnesota First Lady Gwen Walz.
Asked on the eve of the showdown with Vance how his wife had been helping him with debate preparation, Walz told reporters "she wins every one."
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A source familiar with Vance's debate prep tells Fox News Digital that over the last month, the senator took part in a series of murder board sessions with his team, where a group of people who ask tough questions and have candid discussions to help someone prepare for a difficult examination or test, or in Vance's case, a vice presidential debate.
According to the source, Vance conducted a mock debate over the past week, with Rep. Tom Emmer of Minnesota, the House majority whip, playing the role of Walz. Former Trump administration Treasury Department assistant secretary Monica Crowley played the role of one of the moderators from CBS News, which is hosting the debate in New York City.
Halfway through the mock debate, the power went out, as a strong storm slammed through the vicinity of Cincinnati, Ohio, where Vance lives and where the prep session was held. But according to the source, who shared the details first with Fox News, Vance and the team continued on, using lanterns for lighting and cellphones for timers.
Emmer and Walz overlapped for four years in the House before Walz won election in 2018 as Minnesota's governor. "I do know him probably as well or better than most on the Republican side," he said.
And Emmer, taking a shot at his fellow Minnesotan, argued "the hardest part of playing Walz… is trying to tell lies with a straight face, because that’s what he does. He’s good at the debate game, but there isn’t substance there. There’s a lot of air."
Former President Trump, asked Monday if he had given his running mate any advice, told reporters, "No, he doesn't need it."
But he added that he and Vance had "been speaking a little bit back and forth" and that he thought the senator was in "good shape."
Part of the Trump campaign's strategy ahead of the debate is to raise expectations for Walz.
"Walz is very good in debates. I want to repeat that. Tim Walz is very good in debates. Really good. He's been a politician for nearly 20 years. He'll be very well prepared for tomorrow night," Trump campaign senior adviser Jason Miller told reporters on Monday.
Walz comes into the debate with better poll numbers than Vance.
According to the latest Fox News national poll, Walz was slightly above water with a 43% favorable rating and a 40% unfavorable rating.
Vance stood in negative territory, at 38%-50% favorable/unfavorable.
The senator arrived in New York City on Monday afternoon, and in the evening took a break from debate preparations to headline a gathering of GOP mega donors.
Walz was scheduled to fly to New York City on Tuesday, ahead of the debate.
The vice presidential debate is being moderated by "CBS Evening News" anchor and managing editor Norah O’Donnell and "Face the Nation" host and chief foreign affairs correspondent Margaret Brennan.
The 90-minute debate, which kicks off at 9pm ET, will take place at the CBS News broadcast center in New York City.
The Fox News Channel, FOX Business Network, Fox News Digital, Fox News Audio and Fox Nation will air special programming of the debate.
Both the Harris and Trump campaigns agreed to two four-minute commercial breaks during the debate. Campaign staff are not allowed to interact with the candidates during those breaks.
The other rules - including no studio audience - are similar to September's Harris-Trump debate and June's debate between Trump and President Biden.
But there is one major difference - a candidate's microphone won't be muted when the opponent is speaking.
