Which candidates have most to gain — or lose — in first GOP presidential debate?

The first debate among Republican contenders for the GOP nomination for president could be make-or-break for many 2024 hopefuls. But each would-be nominee will face different challenges heading into the showdown.

Florida Gov. Ron DeSantis says he'll be ready on Wednesday night at the first Republican presidential nomination debate. 

"We’ll be ready to do what we need to do to deliver our message, but we absolutely expect that, and we’ll be ready for it," DeSantis said in Fox News Digital interview this past weekend.

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Asked whether his debate strategy includes punching back at rivals on the stage, DeSantis answered, "Yes, that means defending ourselves, but more importantly, showing why we are the leader to get this country turned around."

DeSantis was interviewed on Saturday as he campaigned in the crucial early voting state of New Hampshire. But he's also been fitting in time for debate preparation sessions steered by veteran GOP strategist and debate coach Brett O'Donnell.

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The conservative governor and culture wars crusader is in second place in most 2024 GOP primary polling, trailing former President Donald Trump – who has expanded his commanding lead in the polls over the past six months. But DeSantis is ahead of the rest of the large field of contenders in most polling.

With Trump declining to take the debate stage, DeSantis is likely to come under attack at the showdown.

The Florida governor is trying to change the narrative after a series of setbacks in the past two months, which triggered weeks of negative stories that spotlighted his campaign’s overspending, staff layoffs, change of leadership and other issues.

"I think for Ron DeSantis, this is an opportunity to help reset his campaign and reestablish himself as the clear No. 2," longtime Republican strategist Jim Merrill, a veteran of numerous GOP presidential campaigns, told Fox News.

The Florida governor is far from the only contender on the stage this week at the Fox News-hosted debate in Milwaukee who's prepping for the crucial prime-time showdown. And he's far from the only candidate with plenty on the line.

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Former Vice President Mike Pence, a veteran of two vice presidential general election debates, has been preparing for the first showdown by taking part in mock debates. An adviser who is assisting with those and who asked to remain anonymous in order to speak more freely said Pence "will be very well-prepared."

Pence, by upholding his constitutional duties and overseeing congressional certification of President Biden's 2020 Electoral College victory over Trump on Jan. 6, 2021, amid the assault on the U.S. Capitol, has endured the wrath of the former president and plenty of Trump’s most devout loyalists and supporters.

But the debate, which is expected to draw millions of TV and online viewers, offers Pence a golden opportunity to paint contrasts with the rest of field as he spotlights his conservative stance on numerous key issues, including abortion.

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"We’re ready," Pence senior adviser Marc Short said in a statement. "We’ve been waiting for this for a while."

A source in South Carolina Sen. Tim Scott's political orbit told Fox News that "we’ve brought people in who have deep experience with past campaigns. Tim has been preparing."

Scott, a rising GOP star and the only Black Republican in the Senate, has made his uplifting conservative message the centerpiece of his campaign as he bids for the White House.

"Tim Scott will share his positive, conservative message on the debate stage in Milwaukee," Scott's campaign told Fox News. "This debate is another opportunity to connect with millions of voters across the country and show why Tim has faith in America and why he is the strongest candidate to beat Joe Biden."

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Former New Jersey Gov. Chris Christie – who ran for the 2016 GOP presidential nomination – will be the only candidate on the stage with presidential primary debate experience.

"I'm incredibly relaxed. I've been there before," Christie told reporters this past weekend. "I'll be the only one on that stage that's ever done it before. So, hell, if I'm nervous, they should all be petrified."

Christie, a vocal Trump critic, is expected to take aim at the former president. During a recent interview, Christie said, "I've got a very simple debate strategy. I'll listen to the questions, answer them directly and honestly."

He also said that if a rival candidate says something that he believes "is dishonest," he'll "call them out on it."

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Former U.N. ambassador and former South Carolina Gov. Nikki Haley has been a staple on the campaign trail in the crucial early voting states of Iowa and New Hampshire as well as her home state of South Carolina since launching her presidential campaign in February. She says that experience has helped her prepare for the debate.

"We have done dozens of town halls in Iowa, New Hampshire and South Carolina. We let them ask every question. That’s the best debate prep you can possibly get. So, we’re going to go up on that stage and have a good time," Haley said in a recent Fox News Digital interview.

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But sources in Haley's political world tell Fox News that if she comes under attack at the debate, she'll punch back, but it will be policy oriented. And don't be surprised if Haley spotlights the vast divide on foreign policy between herself and one of her rivals, multimillionaire biotech entrepreneur and political commentator Vivek Ramaswamy. 

Campaign spokesperson Ken Farnaso told Fox News that "Nikki Haley will always stand up for what she believes in."

Ramaswamy – a first time candidate and culture wars crusader – is the biggest surprise in the GOP nomination race so far this cycle. He's seen his support surge and is rivaling DeSantis for second place in some polls. He'll stand center stage with the Florida governor at the debate.

In a Fox News Digital interview last week, Ramaswamy said that "one of the things I’m focused on is not being overly prepared."

Ramaswamy’s campaign told Fox News that the candidate has been cramming in a lot of foreign policy briefings and spars with staff during flights to prepare himself for the initial showdown. But they added that Ramaswamy was not partaking in any mock debates. And on Monday, he said he was getting ready for the debate by playing tennis – shirtless – for a couple of hours.

For former Arkansas Gov. Asa Hutchinson and North Dakota Gov. Doug Burgum, who are anything but household names outside their home states, the debate offers an opportunity.

"This is an opportunity for many of the candidates to make a first impression on the national stage. It also allows candidates who are far back in the pack to have a breakout moment," longtime Republican strategist and communicator Ryan Willams told Fox News.

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Merrill said the candidates are hoping to "create viral breakthrough moments. A moment of strength that gets beyond a 45-second answer about tax policy or farm policy. This is about something that really distinguishes them, a 15-20 second soundbite that grabs voters’ attention and stands out from the clutter."

He added that "in large part, it’s tied to figuring out ways to distinguish themselves on that and also being ready and prepping themselves with people playing the other candidates to make sure that as incoming flak comes at them, they can respond and parry accordingly. It’s really important to be strong up there, be declarative and decisive. They’re all sharpening those 15- and 20-second sound bites and making sure they sound and look commanding on that stage."