Complicating the matter for DeSantis: Trump, the front-runner in the race by far, appears unwilling to provide him with a target.

Trump has said he plans to skip the Aug. 23 debate in Milwaukee. If that happens, DeSantis will likely become the focus of attacks from other candidates looking to climb past him and brand themselves as voters' primary alternative to Trump, according to interviews with rival campaigns, Republican political advisers and a former presidential candidate.

An adviser to Nikki Haley, the former U.S. ambassador to the United Nations who is also seeking the nomination, said the field is likely to treat Trump “gingerly” and instead train their fire on DeSantis, who is expected to occupy the center slot on the stage.

“The guy on the stage on the No. 1 spot is probably going to be taking more heat than the others,” said the adviser, who requested anonymity to discuss internal campaign matters.

Rival campaigns smell blood in the water as DeSantis has faced questions over profligate campaign spending and his readiness for the national stage.

In the most recent Reuters/Ipsos poll, released last week, Trump held 47% of the Republican vote nationally, with DeSantis dropping six points from July down to just 13%. None of the other candidates who will attend the debate have broken out of single digits.

Hotel entrepreneur Robert Bigelow, the biggest individual donor to a group supporting DeSantis' presidential bid, told Reuters on Friday he will not donate more money unless the Florida governor attracts new major donors and adopts a more moderate approach.

Rick Santorum, a former U.S. senator and Republican presidential candidate who participated in a series of debates in the 2012 election, said DeSantis will need to be ready for an “onslaught” of attacks.

During the early primaries when Santorum briefly held center stage as the front-runner, he was widely viewed as having a tough night trying to defend his record in Congress.

“I didn’t prepare to be the center of attention,” Santorum said. “I didn’t prepare enough for the attacks and where the attacks were going to come from. And it cost me.”

DeSantis’ campaign would not comment on his debate preparations.

A former federal attorney who graduated from Harvard Law School, DeSantis can be an effective sparring partner, said Justin Sayfie, who served as a top adviser to Republican Jeb Bush, the former Florida governor and presidential candidate.

“I have to believe he will be well-prepared to punch back hard when he gets punched,” Sayfie said.

In a debate last year during his successful gubernatorial re-election campaign, DeSantis called his opponent, Democrat Charlie Crist, a “worn-out donkey.”

THE TRUMP QUANDARY

Beyond Trump and DeSantis, at least five other candidates appear to be on track to qualify for the debate, including Haley, North Dakota Governor Doug Burgum, former New Jersey Governor Chris Christie, U.S. Senator Tim Scott and entrepreneur Vivek Ramaswamy.

Former Vice President Mike Pence has struggled to reach the debate's requirement of 40,000 individual donors, but his campaign said it is confident Pence will ultimately make it.

Trump has questioned whether he should show up and lend their candidacies credence.

His absence will present a quandary for his lesser-known rivals as they get a chance to introduce themselves to a national television audience of millions: Do they attack Trump in absentia with no risk of return fire or do they focus on those on stage?

With the exception of Christie and Pence, Republican candidates have largely stood by Trump as he has faced a mounting wave of legal troubles, the most recent a four-count federal indictment for conspiring to overturn the 2020 presidential election.

Santorum said the candidates need to take advantage of the moment to go after the front-runner and try to peel off some of his support.

“If I was on that stage, I would be going after Trump,” Santorum said. “That’s where the votes are.”

Aaron Kall, an expert on presidential debates at the University of Michigan, agreed.

“When Trump is not on the stage, it’s time to do it. It’s then or never,” Kall said. "It’s easier when he’s not there, to not have to look him in the eye."

Christie has made clear in interviews that Trump will be his quarry whether or not he is on the stage. Christie has said he will focus on the federal and state cases against the former president and how donors are paying Trump’s legal bills.

A former prosecutor known for his bluntness, Christie famously took down Marco Rubio, a U.S. senator, during a debate in the 2016 presidential race in a moment that was seen as mortally damaging to Rubio’s prospects.

Christie is preparing for both Trump scenarios, a source close to the campaign said, while recognizing most of the pressure at the debate will be on DeSantis to perform, not him.