Olivia Perez-Cubas, a spokesperson for Haley's campaign, said the former South Carolina governor is " the only candidate on the stage who actually has momentum" heading into Wednesday's debate.

"She's in a strong position in all three early states, so for us, it's head down, do the work, be in those early states, meet with voters, share her vision and it's working," Perez-Cubas said on ABC News Live on Wednesday.

Perez-Cubas also said Haley wouldn't be afraid to take on Trump, who has retained his polling lead even as Haley sees her own numbers rise somewhat, while still significantly trailing him.

"When she agrees with Trump, she says it. When she disagrees with Trump, she says it," the spokesperson said. "She makes no qualms about it."

-ABC News' Tal Axelrod

While Ramaswamy has told ABC News White House Correspondent MaryAlice Parks that his plan for the third debate is to "be unhinged," his campaign's deputy communications director separately weighed in on what exactly that strategy means during an appearance on ABC News Live on Wednesday.

"It means that Vivek Ramaswamy at all times speaks the truth. It's the backbone of his campaign ... Vivek Ramaswamy is going to tell the truth in the fact that he's going to put America first, he's not going to lead us into World War III, and at the end of the day every single decision he makes -- and he's going to express this at the debate tonight -- is going to be based on one determining factor: does this put America first?"

Watch the full exchange below.

-ABC News' Alexandra Hutzler

Every candidate goes into a debate hoping for a viral moment or a game-changing performance. But unfortunately for them, that's usually just not how it works.

For instance, according to polling from 538, The Washington Post and Ipsos, the September GOP debate barely changed the minds of any Republican primary voters, and the August one succeeded only in giving Haley a modest boost. As a result, I'm skeptical that any candidate is going to have a breakout moment that will change the trajectory of their campaign.

Even if they have a strong performance and go up in the polls a little bit, like Haley did, they are still facing the reality that Trump is 40 points ahead of his closest competitor. And even if a candidate has a phenomenal debate performance in Miami and surges, say, 15 points in the polls (which would be pretty impressive!), they'd still be at least 25 points behind in the race overall.

-Analysis by Nathaniel Rakich of 538

During the debate, the five GOP candidates will be standing, from audience left to right: Christie, Haley, DeSantis, Ramaswamy and Scott.

Among the debate participants, DeSantis, in the center, is leading in the polls -- ranked second place nationally, according to 538's polling average. He's followed by Haley, Ramaswamy, Christie and Scott in the polls.

Trump continues to lead all of them by double digits.

To be eligible to participate in Wednesday's debate, a candidate must have at least 4% support in two national polls or at least 4% in one nationwide survey as well as two polls from separate early states, based on polls conducted since Sept. 1 that meet the Republican National Committee's criteria for inclusion.

-ABC News' Meredith Deliso