Former President Donald J. Trump won’t be there. But the rest of the Republican field hoping to catch him is now all but set for the first debate of the 2024 presidential primary on Wednesday in Milwaukee.

At least eight candidates have qualified for the stage: Gov. Doug Burgum of North Dakota; former Gov. Chris Christie of New Jersey; Gov. Ron DeSantis of Florida; former Ambassador Nikki Haley; former Gov. Asa Hutchinson of Arkansas; former Vice President Mike Pence; Vivek Ramaswamy, an entrepreneur; and Senator Tim Scott of South Carolina.

A handful of others were on the bubble on Monday night, when the 9 p.m. deadline imposed by the Republican National Committee had arrived for candidates to accumulate at least 40,000 donors and hit 1 percent in a certain number of qualifying national and state polls.

Those with an uncertain status include Perry Johnson, a businessman who previously tried to run for governor of Michigan; Francis X. Suarez, the mayor of Miami; and Larry Elder, a talk-show host who made a failed run for governor of California. All three have said they have enough donors, and Mr. Suarez and Mr. Johnson claim they hit the polling metric, too. But their polling status in the eyes of the party remains less clear.

The R.N.C. has published specific rules about what type of polls count, but because it has not declared particular surveys as acceptable it has left some ambiguity. The party is expected to formally announce who has made the cut on Tuesday.

Republican officials had also required candidates to sign a pledge to support whomever the party nominates. At least one candidate has said he would refuse to sign it: Will Hurd, a former congressman from Texas who has said he opposes Mr. Trump.

With Mr. Trump opting to skip the debate entirely and citing his significant lead in the polls, much of the attention is expected to fall on Mr. DeSantis, who has steadily polled in second place despite some early struggles.

The debate will be broadcast on Fox News at 9 p.m. Wednesday, with Bret Baier and Martha MacCallum serving as moderators.

Despite the candidates’ months of campaigning across the early states of Iowa, New Hampshire and South Carolina already, the debate represents the first moment that many voters will tune into the contest — or even learn about many of the candidates.

“Most of what you do in this process is filtered through media,” Mr. DeSantis said while campaigning in Georgia last week. “Seldom do you get the opportunity to speak directly to this many people.”

Yet it remains unclear how much the debate will transform a race where Mr. Trump remains the prohibitive front-runner, leading the field by large double-digit margins. The hosts have said they plan to turn Mr. Trump into a presence, with quotes and clips from the former president, even though he will not be on the stage. So far, much of the race has revolved around Mr. Trump, with the candidates repeatedly questioned on his denial of the 2020 election results, his four indictments and his role in the Jan. 6 attack on the Capitol.

The other candidates have prepared for weeks. Mr. DeSantis brought on a well-known debate coach, Mr. Pence has been holding practice sessions with mock lecterns in Indiana and Mr. Ramaswamy has been holding sessions with advisers on his private plane (Mr. Ramaswamy also posted a shirtless video of himself smashing tennis balls on Monday, calling it “three hours of solid debate prep”). Only Mr. Christie and Mr. Pence have previously participated in presidential-level debates, giving those two an advantage over less experienced rivals.

Some of those onstage are nationally known, including Mr. Pence, who participated in two vice-presidential debates that were widely watched. But for Mr. Burgum and others, the event will be their national introduction and a chance to sell their biographies or bona fides, such as Mr. Hutchinson, a former congressman who has emerged as one of the party’s most vocal Trump critics.

Breaking through the media attention surrounding the former president will require a viral moment — a surprise attack or notable defense — and the candidates have been reluctant to publicly signal their strategy. The release of memos from Mr. DeSantis’s super PAC last week was viewed as a significant tactical error that heightened the pressure on the Florida governor while limiting his avenues of attack.

Some of Mr. Trump’s rivals have mocked him for skipping the debate, with Mr. Christie calling him a “coward.” Those taunts were unsuccessful in luring Mr. Trump in, though Mr. Christie has signaled his eagerness to swing at him in absentia.

It is far from clear how much fire the rest of the field will focus on the missing front-runner, or whether they will skirmish among themselves in a bid to claim second place as his leading challenger.

Mr. DeSantis’s aides have said they expect him to bear the brunt of attacks on Wednesday because he will be the leading candidate on the stage.

Mr. Scott and his allies have aired a heavy rotation of advertising in Iowa and he has risen there to third place in some polling, including a Des Moines Register/NBC News survey this week. But those ads have not helped him catch Mr. DeSantis yet, let alone Mr. Trump.

Ms. Haley, the former governor of South Carolina before she served as ambassador under Mr. Trump, has sought to find middle ground, arguing that the party needs to move past the former president yet doing so without being overly critical of an administration she served in.

Mr. Pence has searched for traction in a race where he has been typecast as a betrayer to Mr. Trump by some voters, for standing up to his bid to block certification of President Biden’s victory. That confrontation has established Mr. Pence as a critical witness in one federal indictment against Mr. Trump.

Mr. Trump, of course, is not giving up the spotlight entirely. He has recorded an interview with Tucker Carlson, the former Fox News host, as counterprogramming to the network’s debate. And on Monday his lawyers agreed to a $200,000 bail ahead of his expected surrender to the authorities in Georgia later this week after he was charged as part of a criminal conspiracy to overturn the election result there in 2020.

The criminal indictment was Mr. Trump’s fourth of the year, though the accumulation of charges has done little to slow or stop his consolidation of support in polls so far.