Less than a month before the first Republican primary debate, the Republican National Committee already is raising the bar on its requirements for the second debate, set for late September.

The second Republican debate is scheduled on September 27 at the Ronald Reagan Presidential Library at Simi Valley, California. The criteria for the second debate were disclosed by the RNC chairwoman, Ronna McDaniel, on Fox News Wednesday morning.

The RNC will require candidates to poll at 3 percent in two national polls or 3 percent in one national poll and 3 percent in two early-state polls, meaning Iowa, New Hampshire, South Carolina, and Nevada.

“Once you get on the debate stage and you get in front of the American people, if you’re not having momentum, if you’re not showing growth in your campaign, then that’s a problem,” Ms. McDaniel told Fox News. “And we need to make sure that we are putting in front of the Republican primary voters the candidate who is going to take on Joe Biden.”

This requirement is a step up from the polling requirement for the first debate, set for August 23, which was 1 percent in two national polls or 1 percent in a national poll and two early-state polls.

The RNC also raised the requirements in terms of donors, with the second debate requiring 50,000 unique donors, with at least 200 each in 20 different states or territories. The requirement for the first debate is 40,000 donors.

Candidates will also be required to pledge to support the eventual Republican nominee and to not participate in debates other than those hosted by the RNC.

So far, President Trump, Governor DeSantis, Ambassador Haley, Senator Scott, businessman Vivek Ramaswamy, Governor Christie, and Governor Burgum have qualified for the first debate.

One major candidate who has not yet qualified for the first debate is Vice President Pence, though he maintains that he expects to do so before the deadline, which is 48 hours in advance of the event.

Other candidates, like Governor Hutchinson, also haven’t qualified for the debate. Congressman Will Hurd doesn’t plan to attend because he refuses to sign the pledge to support the eventual nominee. 

The loyalty pledge has been a sticking point in the run-up to the debate, with Mr. Christie saying that he will respect it as much as Mr. Trump did in 2016, when Mr. Trump abandoned the pledge after the field narrowed to three candidates. Mr. Hutchinson has also expressed distaste for the loyalty pledge.

Looming over the conversation around the debate is that Mr. Trump says he will not attend. Mr. DeSantis has mocked Mr. Trump for his position, but it’s not clear whether it will affect his decision.

“You have got to earn the nomination … doing things like these debates, they’re important parts of the process,” Mr. DeSantis said in an interview with a radio host, Howie Carr. “I’ll be at all the debates because the American people deserve to hear from us directly about our vision for the country.”

While Mr. Trump may make a last-minute decision to attend the debate, an advisor close to Mr. Trump, Jason Miller, told NewsNation that it “really wouldn’t make much sense for him to go and debate right now,” given the other candidates’ low levels of support.

“At the moment, President Trump has indicated that he’s unlikely to participate, at least in the first two debates,” Mr. Miller said. “So ultimately, President Trump will make a decision as we get closer. He has not said anything definitive, one way or the other. I’m not expecting him to participate, though.”

If Mr. Trump ultimately sticks with his decision to not attend the debate, it would remove a major opportunity for other candidates, all of whom have a lot of ground to cover in the polls in order to catch up with the frontrunner, to confront the former president. 

As it stands, the only path to the Republican nomination is to pull support from Mr. Trump. In the latest poll of 3,714 likely voters from Morning Consult, conducted between July 28 and 30, Mr. Trump maintains 58 percent support.

The next most popular candidate is Mr. DeSantis, who enjoys 15 percent support, and then Mr. Ramaswamy, also at 15 percent.