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

At the beginning of the year, DeSantis was the clear runner-up in the Republican presidential primary field: He was averaging above 30% in national polls, only about 10 points behind Trump. But DeSantis’ star has fallen the more voters have gotten to know him, it seems, and another candidate is now on the verge of overtaking him as the most viable Trump alternative: Haley.

As of Tuesday, Haley was at 11% in 538’s national polling average of the Republican primary -- just 2 points behind DeSantis for second place. And she’s doing even better in early primary states. She’s polling at 15% in Iowa, and she’s comfortably in second place in New Hampshire (19%) and South Carolina (21%).

She also recently secured the endorsement of Americans for Prosperity Action, a conservative group affiliated with Republican megadonor Charles Koch that is known for its sophisticated political operation.

Why has Haley been on the upswing? The simplest explanation is these debates. On the day of the first debate, she was averaging just 3% in national polls. But according to a 538/Washington Post/Ipsos poll conducted both before and after that debate, Republicans who watched said Haley was one of the strongest performers, and the share who said they were considering voting for her shot up by 17 points.

Republican debate watchers also rated Haley as the second-best performer in the second debate and the strongest performer in the third debate. Probably not by coincidence, her polling numbers have been steadily increasing ever since.

Of course, Haley fans shouldn’t get too giddy. She (and DeSantis) are still far behind Trump both nationally and in the early primary states. Even if Haley does overtake DeSantis and winds up being the last non-Trump Republican standing in the primary, it won’t matter if Trump is winning every state by double digits.

-Analysis by Nathaniel Rakich of 538