To participate in the first Republican presidential debate on Aug. 23, candidates must meet challenging new criteria, including having at least 40,000 donors and voter support of at least 1 percent in three approved polls. But the requirement causing the most consternation is a pledge to support the eventual nominee.

The candidates will be sent the pledge only after meeting the other qualifications, according to a person familiar with the process, and will have until 48 hours before the debate to meet those criteria, giving them until the last minute to make up their minds. Here is what they have said:

Donald J. Trump

Unclear. Former President Donald J. Trump has not said whether he will sign the pledge.

In February, he refused to commit to supporting the eventual nominee, telling the conservative radio host Hugh Hewitt, “It would have to depend on who the nominee was.” But that was before the Republican National Committee made the pledge a debate requirement.

Even if he signs, it is unlikely to mean much. He signed the same pledge in 2015 and then reneged on it.

Ron DeSantis

Unclear. Asked last month whether he would support Mr. Trump in a general election, Gov. Ron DeSantis of Florida didn’t give a straight answer.

Mr. DeSantis vaguely indicated he might make the pledge, saying, “You respect the process, and you respect the people’s decisions.” But he made no commitment.

Doug Burgum

Yes. Gov. Doug Burgum of North Dakota has indicated that he will sign the pledge.

“I’m going to support whoever the Republican candidate is going forward in 2024,” he told ABC News.

Chris Christie

Mixed messages. Former Gov. Chris Christie of New Jersey has suggested he will sign the pledge: “I will do what I need to do to be up on that stage,” he told CNN.

“I’m going to take the pledge just as seriously as Donald Trump took it in 2016,” he said, adding that he considered it “useless” and had told the R.N.C. as much.

Nikki Haley

Yes. Nikki Haley, the former governor of South Carolina and former United Nations ambassador, has committed to signing the pledge.

“Absolutely irresponsible that Trump, DeSantis, and others won’t commit 100% to supporting the Republican nominee,” she wrote on Twitter. “There’s no room for personal vendettas in this battle to save our country.”

Will Hurd

No. Former Representative Will Hurd of Texas is the only candidate who has ruled out signing the pledge.

“I can’t lie to get access to a microphone,” he told CNN, adding: “I’m not going to support Donald Trump. I recognize the impact that it has on my ability to get access to the debate stage, but I can’t lie.”

Asa Hutchinson

Mixed messages. Former Gov. Asa Hutchinson of Arkansas has ruled out voting for Mr. Trump if he is convicted of a felony, but said he would sign the pledge out of confidence that Mr. Trump wouldn’t win the primary.

“You would have to make the pledge based on the fact that Donald Trump is not going to be our nominee and you’re confident of it,” he told ABC News.

He asked the R.N.C. to “clarify that there is no pledge to support a nominee if they are found guilty of espionage or a serious felony.” (The R.N.C. said no.) At the same time, he says he will do whatever is required because the debates are important.

Mike Pence

Mixed messages. Former Vice President Mike Pence initially seemed to commit during a CNN town hall event, saying, “I’ve always supported the Republican nominee for president in the United States, and I’ll support the Republican nominee in 2024.”

But he struggled to reconcile that with his assertion that “anyone who puts themselves above the Constitution,” as he says Mr. Trump did, “should never be president.”

He said he did not believe that Mr. Trump would win and dodged follow-up questions. “I don’t think my old running mate is going to be the Republican nominee for president, and I’m very confident, very confident, that we’ll be able to support the Republican nominee,” he said, suggesting that he might not if it is Mr. Trump.

Vivek Ramaswamy

Mixed messages. The entrepreneur Vivek Ramaswamy has waffled on the pledge.

In February, he said he would make it. But last month, he gave a caveat: “If the other candidates in this race make that pledge, I will stand by and be willing to,” he told Fox News, adding, “I’m ready to play ball, but I require the other candidates to play ball as well.”

Tim Scott

Yes. Senator Tim Scott of South Carolina has indicated that he will sign.

“All Republican candidates would be better than any Democrat candidate,” he told Fox News, while saying he was confident he would win the nomination.

Francis Suarez

Yes. Mayor Francis Suarez of Miami didn’t vote for Mr. Trump in 2020 but says he will sign the pledge.

“I think every single Republican candidate who wants to be on the debate stage has to pledge to support the nominee, and I will do that as well,” he told ABC News.