While Christie has largely run in the primary as the biggest critic of Trump from within the GOP, polls show his message hasn't moved many voters.

Pressed on this on the debate stage, Christie sought to play down his low approval ratings from the party and suggested it was because he was telling the "truth" about Trump and Republicans, he said.

"He is unfit," he said of Trump, calling Trump a "dictator."

The former president -- his record, his rhetoric and his front-runner status in the race -- have to be discussed head-on, Christie said.

"There is no bigger issue in this race," he said.

-ABC News' Adam Carlson

Ramaswamy joined DeSantis in keeping the debate's early fire trained on Haley, accusing the former U.N. ambassador of bowing to corporate interests and taking money from prominent Democratic donors. Ramaswamy was fielding a question from Kelly on his own temperament and penchant for insults, which the SiriusXM host said has fluctuated from one debate to the next, and to which Ramaswamy acknowledged “there’s a time and place for everything.”

Ramaswamy then said Haley went from bankruptcy to being a high earner after her government service. Haley responded that her earnings in public life “may be bankrupt to him, but it wasn’t bankrupt to us.” She fired back at both Ramaswamy and DeSantis on her donors: “They’re just jealous. They wish they were supporting them.”

-ABC News' Chris Boccia

In his first answer, DeSantis dismissed the polls by saying that they showed that a “red wave” was going to happen in the 2022 midterms. In reality, though, most polls didn’t show that: For example, 538’s final average of polls of the generic congressional ballot said that Republicans were leading by just 1 point nationally. They ended up winning by 3 points.

-Analysis by Nathaniel Rakich of 538

The first question of the night went to DeSantis, who was asked about his stagnating poll numbers and whether voters are telling him "not no but not now."

"So we have a great idea and American voters actually make these decisions, not pundits or pollsters," he responded, adding he's "sick" of hearing about the polls.

"The voters are going to be able to speak and we're going to earn this nomination," he continued. "I am sick of Republicans who are not willing to stand up and fight back against what the left is doing to this country. You've got to be willing to stand strong and you've got to be willing to beat these people."

-ABC News' Alexandra Hutzler

Can anyone take down Haley? According to 538’s polling with The Washington Post and Ipsos, Republican primary voters have responded favorably to each of Haley’s first three debate performances, and it’s probably not a coincidence that she’s been rising in the polls at the same time. But that could put a target on her back on Wednesday -- and it’s possible that her momentum will stall if she’s perceived to have a bad performance.

Will anyone go after Trump? So far, the debates have mostly consisted of the candidates on stage attacking each other. But that’s an odd strategy considering that their biggest obstacle to the nomination is Trump. In fact, he’s above 50% in 538’s national polling average -- meaning that even if another candidate consolidates all of the non-Trump vote, Trump would still be ahead. That means that someone is going to have to peel support away from Trump in order to win the nomination -- and one way to do that is to attack him in the debates.

Who will perform best on the economy and immigration? According to the latest 538/Washington Post/Ipsos poll, 52% of likely Republican voters said getting inflation or costs under control was one of the top three issues in determining their primary vote; 41% said controlling immigration was one of their top three issues. These will probably be the most important segments to watch at the debate then: If a candidate really aces a question on inflation or immigration, that could go a long way.

Will anyone watch? The ratings have been falling with every debate: While the August faceoff garnered 12.8 million viewers, the September one got 9.5 million and the November one got only 7.5 million. And only 26% of the respondents to our 538/Washington Post/Ipsos poll said they were very likely or absolutely certain to watch the fourth debate. Obviously, the fewer people who watch the debate, the less anything that happens on stage will matter.

-Analysis by Nathaniel Rakich of 538