(NEXSTAR) – Tighter qualifications, a narrowing field of candidates and one significant “no” from the RSVP list meant only four Republican presidential challengers took the stage in Tuscaloosa, Alabama, on Wednesday as NewsNation hosted the fourth GOP debate.

Florida Gov. Ron DeSantis, conservative entrepreneur Vivek Ramaswamy, former United Nations Ambassador Nikki Haley and former New Jersey Gov. Chris Christie shared the spotlight at Moody Music Hall on the University of Alabama campus beginning at 8 p.m. Eastern Time.

The two-hour debate was moderated by NewsNation’s Elizabeth Vargas; Megyn Kelly, host of “The Megyn Kelly Show” on SiriusXM, and Eliana Johnson, editor-in-chief of The Washington Free Beacon.

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With just over a month before the 2024 primary calendar begins, the debate demonstrated how firm Trump’s grip remains on the party.

But the focus on Haley reflected how other candidates perceive her as a threat to their chances of taking on Trump directly. Aside from former New Jersey Gov. Chris Christie, most of the candidates have spent more time in debates going after each other than taking aim at Trump, reflecting the former president’s popularity among Republicans and what many see as diminishing returns in attacking him.

Trump remains dominant in national and early-state polls. And after holding counterprogramming rallies during the first three debates, he didn’t bother this time and instead went to a closed-door fundraiser. His campaign posted an ad during the debate focusing on President Joe Biden as both parties head toward a potential rematch of the 2020 election Trump lost.

Christie repeatedly tore into Trump on Wednesday and challenged Florida Gov. Ron DeSantis to answer directly if he believed Trump was fit or unfit to be president again. The crowd at the University of Alabama booed him at one point as he attacked Trump.

“His conduct is unacceptable. He’s unfit. And be careful of what you’re going to get,” warned Christie, who has been alone among leading Republicans in his focus on the race’s clear front-runner.

“There is no bigger issue in this race than Donald Trump,” he said earlier.

DeSantis suggested Trump, who is 77, is too old for the job.

“Over a four-year period, it is not a job for someone that’s pushing 80,” DeSantis said. “We need someone who’s younger.”

Biotech entrepreneur Vivek Ramaswamy again raised his hand as a candidate who would support Trump even if he were convicted in any of the four felony indictments he faces. Ramaswamy accused his other opponents of bowing to Trump for years to secure political posts or financial gain, but the closest the 38-year-old ever came to criticizing Trump was to call for a new generation of leadership.

Haley stood silently during the extended discussion, and neither the moderators nor her rivals asked for her opinion.

The debate’s brief focus on Trump was a reprieve for Haley, who spent most of the debate on the defensive.

DeSantis accused Haley of backing down from media criticism and Ramaswamy suggested she was too close to corporate interests as she gets new attention from donors. He touted his own willingness to pick high-profile fights with his critics and went after Haley just moments into the debate, reflecting the rivalry between the two candidates reflected in dueling early-state television ads.

They also tussled over China, long an animating issue for conservatives worried about Beijing’s influence. Later in the debate, Haley credited Trump for taking a hard line with Beijing on trade but said he was too passive on other fronts, including allowing China to capture American technology for its own military use and purchase American farmland.

Interrupting Haley, DeSantis accused her of allowing Chinese investment in South Carolina when she was governor and suggested her corporate donors would never allow her to be tough on Beijing.

“First of all, he’s mad because those Wall Street donors used to support him and now they support me,” Haley retorted before accusing DeSantis of being soft on Chinese investment in Florida.

Ramaswamy, always the most eager to deliver personal barbs on the debate stage, turned a foreign policy discussion into another attack on Haley, seemingly trolling her to name provinces in Ukraine and suggesting she does not understand the country. As he kept piling on, Christie stepped in to declare Haley “a smart, accomplished woman” and dismiss Ramaswamy as “the most obnoxious blowhard in America.”

To qualify for the Tuscaloosa debate, candidates had to register at least 6% in two national polls or 6% in one national poll and two early-voting states, including Iowa, New Hampshire, South Carolina and Nevada.

Candidates also needed to obtain at least 80,000 unique donors with at least 200 from 20 states and U.S. territories. They are also required to sign a loyalty pledge, promising to support the eventual nominee.

The Associated Press contributed to this report.