Harris and Trump face off in historic debate, experts point to 'High, high stakes'

In what may be the defining moment of the 2024 presidential election, Vice President Kamala Harris and former President Trump face off Tuesday in their first and potentially only debate.

And with a margin of error race with eight weeks to go until Election Day and early voting getting underway this month in some crucial battleground states, there's no denying how much is on the line as Harris and Trump face-off for 90 minutes in primetime at Philadelphia's National Constitution Center.

"It's high, high, high stakes. This is going to be a really, really important moment in the campaign," longtime Republican strategist and veteran of numerous GOP presidential campaigns David Kochel told Fox News Digital.

With the presidency up for grabs, the intense jockeying by both candidates and their camps has been heating up ahead of the debate.

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"There's no floor for him in terms of how low he will go. And, and we should be prepared for that. We should be prepared for the fact that he is not burdened by telling the truth," the vice president charged in a radio interview on the eve of the debate.

The comment appeared to be the latest stab by Harris to roil Trump in the days leading up to the showdown.

Hours later, on Tuesday morning, another jab, as the Harris campaign launched a new ad that spotlights Trump's age and seeming obsession with crowd sizes, as it used clips from former President Barack Obama's much-talked about tweaks of Trump during his Democratic National Convention speech last month.

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Trump has repeatedly insulted the vice president over her intelligence, mockingly nicknamed her ‘Comrade Harris,' and even questioned her racial identity in the month and a half since Harris replaced President Biden atop the Democrats' 2024 ticket.

And Trump, using familiar tactics, has been laying the groundwork for what he calls a "rigged" debate as he has repeatedly blasted ABC News - the host of the 90-minute face-off, and accused the networks' top talent of being biased against him.

The debate comes as Harris has enjoyed a wave of momentum in both polling and fundraising after taking over as the Democrats' standard-bearer, but the Trump campaign counters Americans' honeymoon with the vice president is subsiding.

CLICK HERE FOR THE LATEST FOX NEWS REPORTING ON THE HARRIS-TRUMP DEBATE

Biden's disastrous performance in his late June debate against Trump instantly fueled questions about his physical and mental abilities to serve another four years in the White House - and spurred a rising chorus of calls from within his own party for the 81-year-old president to end his bid for a second term. Facing increased pressure from fellow Democrats, Biden, in a blockbuster announcement on July 21, ended his re-election campaign and endorsed his vice president.

"I don't know if we'll ever see a debate that was more consequential than the one that drove Biden from the race, but if there is one, it would be this one," Kochel emphasized.

Pointing to the latest national and key battleground state polls, which indicate a margin-of-error race, he pointed out "this race has settled into an absolute tie, and this may be the only real point that can create a dynamic where these candidates can move up or down."

Harris and Trump are taking vastly different approaches to preparing for Tuesday's showdown.

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Harris spent most of the past four days hunkered down in a downtown Pittsburgh hotel, taking part in an intensive "debate camp," which included numerous mock debate sessions. She arrived in Philadelphia on Monday evening, 24 hours ahead of the debate.

Trump spent much of this past weekend at his golf club in Bedminster, New Jersey, taking part in less formal ‘policy sessions’ with aides and allies. But Trump also traveled to swing state Wisconsin on Saturday to headline a campaign rally. 

Fox News learned that Trump would be spending Tuesday huddling with advisers at his Mar-a-Lago club in Palm Beach, Florida, before flying to Philadelphia just a couple of hours before the start of the 9pm ET debate, which will be simulcast on the Fox News Channel.

"Trump is prepared for every style because that's what he's been doing on the campaign trail; has been doing unscripted pressers, pull-asides, interviews," Trump campaign senior adviser Jason Miller told reporters on the eve of the debate.

The former president has repeatedly criticized Harris for sitting for only one major interview, and holding no news conferences, since taking over for Biden as the Democrats' standard-bearer. And on the eve of the debate, the Trump campaign announced that the former president will hold another news conference Friday in Los Angeles.

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Both candidates come into the debate aiming to achieve certain goals.

For Harris, job number one is doing no damage by avoiding major gaffes. Another goal - appealing to the remaining undecided voters in the race and neutralizing Trump's repeated accusations that the vice president is more liberal than progressive rockstars Sens. Bernie Sanders and Elizabeth Warren.

Up for discussion - how much Harris will need to push back on Trump's misstatements.

Maryland Gov. Wes Moore, a top Harris surrogate and a rising star in the Democratic Party, told reporters on Monday that I think he thinks the vice president "is not going to spend her time fact checking Donald Trump. I don't think that's a useful exercise."

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And Moore said that Harris, who is much less well known to Americans than Trump, needs to "spend her time presenting her vision for what the future of this country is."

A top job in the debate for Trump, who faces a large polling deficit among women voters, is to avoid further insulting Harris, who if elected would make history as the nation's first female president.

Also high on Trump's to-do list, effectively tie Harris to Biden, who's approval ratings remain well underwater as Americans continue to deal with lessening but persistent inflation. 

"She can run, but she cannot hide from her tenure during the Biden administration," senior Trump campaign adviser Corey Lewandowski said Monday on Fox News ‘The Story.’ "So when you look at what this debate's going to be, it's going to be the opportunity for Americans to see two candidates who have a fundamentally different view of what this country should look like."

Sen. Tom Cotton of Arkansas, a Trump ally, told Fox News Digital that "the American people know where President Trump stands. They know what they got when President Trump was president."

Pointing to the vice president, Cotton charged that "Kamala Harris has tried to run as a blank slate."

Texas Gov. Greg Abbott, another Trump ally, said his advice to the former president is "let Harris talk."

"The more she talks without talking into a teleprompter, the more she shows America that she’s really not up to the task," the three-term governor argued in a Fox News Digital interview.

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Republican consultant and Fox News contributor Ari Fleischer, a former White House Press Secretary in then-President George W. Bush's administration, said that Trump needs to "hit her on policy. Just like you did to Biden in the first debate. That was a disciplined, tough, policy-oriented Donald Trump. I would love to see the same Donald Trump against Kamala Harris." 

But a big question heading into the debate is whether Trump will listen to the advice he's getting, and if he can stay disciplined throughout the showdown.

"Trump is going to be himself," Miller told reporters.

After plenty of debate over the debate, both camps agreed to adhere to the same rules that governed the Biden-Trump debate.

The most contentious rule - the microphones will once again be muted during an opponent's responses, which pundits see as a victory for Trump. 

And as with the June debate, there will be no studio audience.

Both candidates will be supplied with a pen, pad, and a bottle of water, but are not allowed pre-written notes or props - and will not be allowed to talk with their campaign staff during the debate or during the commercial breaks.

The moderators, ABC News' David Muir and Linsey Davis, will be the only ones asking questions, according to the rules.

Post-debate, Harris gets right back on the campaign trail, with stops in some of the crucial battlegrounds, starting with two rallies Thursday in North Carolina.

"It is certainly an important moment in the campaign, but it is one moment," longtime Democratic strategist and presidential campaign veteran Maria Cardona told Fox News Digital. "It was a margin of error race going into the debate, and it will be that afterward," 

Trump also quickly gets back on the trail, with a stop Thursday in swing state Arizona.

Get the latest updates from the 2024 campaign trail, exclusive interviews and more at our Fox News Digital election hub.