DeSantis went after Haley's conservative record, saying she "caves any time the left comes after her" and claimed she opposed a Florida bill prohibiting gender-affirming medical care for minors.

Haley countered that she actually opposed the Parental Rights in Education Act that limited discussion of sexual orientation and gender identity in some of Florida's K-12 classrooms, dubbed by its critics as the "Don't Say Gay" bill, because it "didn't go far enough."

"It only talked about gender until the third grade, and I said that it shouldn’t be done at all, that that's for parents to talk about, shouldn't be talked about in schools," she said.

She mentioned that the "most conservative grassroots group in the country" -- Americans for Prosperity Action -- endorsed her last week.

DeSantis followed up by continuing to claim that she opposed a Florida bill prohibiting gender-affirming medical care, such as puberty blockers, on minors.

"That is what Nikki Haley opposed. She said the law shouldn't get involved in that," he said. "And I just asked you, if you're somebody that's going to be the president of the United States and you can't stand up against [that], how are you going to be able to stand up for anything?"

At a town hall in February Haley said she did not think the so-called Don't Say Gay bill "goes far enough," Fox News reported.

-ABC News' Meredith Deliso

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

As the debate turned to bans on gender-affirming medical treatments for minors, Christie offered a different view than the three other candidates on stage.

He said it should be a parent's decision, not the decision of the government.

"We should empower parents to be teaching values that they believe in their homes without government telling them what those values should be," he said. "Yet we want to take other parental rights away. I'm sorry, but as a father of four, I believe there is no one who loves my children more than me. There is no one who loves my children more than my wife. There is no one who cares more about their success in health, in life than we do, not some government bureaucrat."

Christie added: "This is not something I favor. I think it is a very, very dangerous thing to do. But that's my opinion as a parent. I get to make the decisions about my children, not anybody else."

Other candidates dove straight into their opposition to gender-affirming care for minors.

DeSantis said, "You do not have the right to abuse your kids." Ramaswamy said his view is that "transgenderism is a mental health disorder," which fact-checkers have challenged.

-ABC News' Alexandra Hutzler