Who Will Attend the First Republican Debate? What We Know About Trump and His Rivals.

With a month to go before the first Republican presidential debate, the stage in Milwaukee remains remarkably unsettled, with the front-runner, former President Donald J. Trump, waffling on his attendance and the rest of the participants far from certain.

Gov. Ron DeSantis of Florida is in. So are Nikki Haley, the former governor of South Carolina, Senator Tim Scott of South Carolina, and Vivek Ramaswamy, the entrepreneur and author. Chris Christie, the former New Jersey governor and scourge of Mr. Trump, said he would be on the stage as well.

But the Republican National Committee’s complicated criteria to qualify for the Aug. 23 gathering — based on candidates’ donors and polling numbers — have also created real problems for others in the field.

Former Vice President Mike Pence, who would be a serious candidate for the Republican nomination by most measures, may not be invited to debate because of the R.N.C.’s measures: Candidates must have at least 40,000 individual donors, and 1 percent in three national polls of Republican voters, or 1 percent in two national polls and two polls in the early primary states.

The debate in Milwaukee — the first of three scheduled so far — has been billed by the party and the candidates as an inflection point in a race that has remained in stasis, even with its front-runner under state and federal indictment, with more charges expected soon. Mr. Trump is likely to face charges next month stemming from his efforts to overturn President Biden’s 2020 victory in Georgia, and has been notified that he could be indicted soon on federal charges for clinging to power after his electoral defeat.

Yet he remains the prohibitive leader in state and national polling, with Mr. DeSantis a distant second and the rest of the field clustered in single digits.

The debate will offer the dark horses perhaps their last shot at making an impression, if they can qualify, and all candidates not named Trump a chance to present themselves as the true alternative to the legally challenged former president. Over the next month, political observers will see a steady taunting of the front-runner by candidates who see a no-lose scenario. Either they goad Mr. Trump to share the stage with them, giving them equal billing with the front-runner and a chance to take a shot at him, or they paint him as too scared to show up, denting his tough-guy image.

“As Governor DeSantis has already said, he looks forward to participating in the debates and believes Trump should as well — nobody is entitled to this nomination; they must earn it,” said Bryan Griffin, a spokesman for the DeSantis campaign.

On CBS’s “Face the Nation” on Sunday, Mr. Christie promised, “I’ll be on this stage for all of the debates, and I will hold Donald Trump personally responsible for failing us.”

For his part, Mr. Trump has stayed noncommittal. Senior advisers have counseled him against showing up and validating his challengers, but his rivals believe they can prick his ego and shame him to the stage.

“You’re leading people by 50 or 60 points, you say, why would you be doing a debate?” Mr. Trump said on Fox News last weekend. “It’s actually not fair. Why would you let someone who’s at zero or one or two or three be popping you with questions?”

In some sense, the Milwaukee debate is haunted by the circuslike atmosphere that pervaded the Republican debates of 2015 and 2016, when Mr. Trump ran roughshod over crowded stages with insulting nicknames and constant interruptions. At one point, the discussion devolved into lewd references to the significance of the size of Mr. Trump’s hands.

The Republican National Committee’s thresholds were intended to keep the number of participants down and ensure that only serious candidates made the stage. The final roster will not be set until 48 hours before debate night, when the last polls come in and the candidates must pledge that they will back the eventual Republican nominee.

But with a month to go, the polling and donor thresholds — imperfect as they may be — are already narrowing the field.

Ronna McDaniel, the chairwoman of the R.N.C., said Friday on Fox Business that a candidate who cannot win over “40,000 different small dollar donations” is “not going to be competitive against Joe Biden.”

Candidates like Mr. Ramaswamy and Mr. Scott have used the donor rules to tout the power of their campaigns beyond the single digits they have garnered in national polling.

“Tim will be on the debate stage for months to come thanks to over 145,000 donations from over 53,000 unique donors across all 50 states,” said Nathan Brand, a spokesman for the Scott campaign.

Long-shot candidates like the Los Angeles commentator Larry Elder, Mayor Francis X. Suarez of Miami, former Representative Will Hurd of Texas and the businessman Perry Johnson are not likely to make the cut.

In an interview on Friday, Mr. Elder said he was only about halfway to the donor threshold, and because his name is often omitted from Republican polling, reaching 1 percent could be impossible. For candidates like him, he conceded, making the stage is existential for his campaign.

“It’s crucial for me to get on that debate stage; that’s Plan A, and Plan B is to make Plan A work,” he said, suggesting there is no other option.

Some candidates, like Mr. Pence and Asa Hutchinson, the former governor of Arkansas, could also fall short of qualifying. Mr. Pence, who has easily cleared the polling threshold but has badly lagged in fund-raising, launched an email blitz on Wednesday, pleading for 40,000 people to send his campaign $1. Mr. Hutchinson is still short of 40,000 but did reach 1 percent in a qualifying national poll this month.

Doug Burgum, the governor of North Dakota, may still qualify, in part because Mr. Burgum, a wealthy former software executive, is offering $20 gift cards to the first 50,000 people who donate at least $1 to his campaign. He is also pumping up his standing in early-state polls with a well-financed ad blitz.

“Gov. Burgum will absolutely be on the debate stage next month,” said his spokesman, Lance Trover.

Mr. Burgum is not alone in his creative fund-raising strategies. Mr. Ramaswamy, who like Mr. Burgum is wealthy enough to self-fund his presidential bid, is offering donors a 10 percent cut of the donations they get from those they convince to give to the Ramaswamy campaign. Mr. Suarez last week said he would enter anyone who sends his campaign $1 into a raffle for Lionel Messi’s first game with Inter Miami, the South Florida Major League Soccer club.

“It corrupts the process. It makes us look foolish. It makes us look silly,” said Mr. Elder, who accused the R.N.C. of stacking the deck for elected officials and the super rich.

Mr. Christie is making something of a mockery of another R.N.C. demand — that every candidate sign a pledge to back the eventual nominee. Mr. Christie, who was once a confidant of Mr. Trump’s and is now his sworn enemy, has said he will sign the pledge, but he has added that he will take the promise as seriously as Mr. Trump takes his promises — that is to say, not seriously at all. In the spring of 2016, Mr. Trump reneged on a similar pledge, though it became moot when he secured the nomination.

Karl Rickett, a spokesman for Mr. Christie, said on Friday that the former governor had not swerved from that stand.

Mr. Hurd has said flat out that he will not sign the pledge, but there is little indication he can make the debate stage anyway.

For his part, Mr. Trump may make a mockery of the debate itself. In 2016, he skipped a Republican primary debate over his feud with the Fox New host Megyn Kelly and “counterprogrammed” a benefit for veterans in Des Moines. On his Truth Social media site on Sunday, Mr. Trump said “so many people have suggested” that he debate the former Fox News star Tucker Carlson on the night of the first Republican debate.

Aides to rival campaigns last week said the Republican National Committee should place sanctions on Mr. Trump if he pulls a similar stunt in August.

Whether Mr. Trump shows up or not, he will be the target of his rivals for the next four weeks. And if the former president does not show, he still could attend the debate at the Ronald Reagan Library in Simi Valley, Calif., in September, or the one in Alabama in October.

Mr. Christie’s super PAC, Tell It Like It Is, is already running advertisements mocking Mr. Trump’s reluctance. And others are jumping in.

“We can’t complain about Biden not debating R.F.K. if Trump is not going to get on the debate stage and stand next to us,” Ms. Haley said last week, referring to the president and Robert F. Kennedy Jr., who has challenged Mr. Biden for the Democratic nomination.

“I have never known him to be scared of anything,” she said of Mr. Trump. “I certainly don’t expect him to be scared of the debate stage, so I think he’s going to have to get on there.”