Haley lamented the state of economy, promising to veto any spending bill that doesn’t take federal expenditures to pre-COVID-19 levels. She slammed the Trump administration for adding $9 trillion to the federal debt.

DeSantis wouldn’t directly target Trump but chalked the the problem up to “both parties in Washington, D.C. That’s just a fact.” He pointed to student loans as an economic backbreaker for young people and touted his record on vocational education, which he said could encourage universities to become more accessible: “Don’t let anybody tell you the only way you can be successful is through a four-year, brick-and-ivy degree. That’s one way you could be, not the only way, and we’re gonna fix that problem in the United States of America.”

- ABC News’ Chris Boccia

The early back-and-forths in this debate showed an interesting dynamic between Haley-Christie and, more subtly, DeSantis-Ramaswamy. Ramaswamy has been going after Haley hard, arguably doing some of DeSantis's work for him, while Christie found himself defending Haley from Ramaswamy's attacks.

What's interesting about this, beyond the fireworks, is where Christie and Ramaswamy supporters might go as this race proceeds, as neither candidate looks to have much chance of winning the GOP nomination (to put it mildly).

Ramaswamy is closely aligned with the Trump wing of the party, which DeSantis is also part of, so some Ramaswamy supporters might look at DeSantis as a preferable option (if they don't want Trump). Meanwhile, Christie's supporters are the least Trumpy, so if he goes by the wayside, they probably would prefer Haley -- a more traditional Republican -- over DeSantis, Ramaswamy and certainly Trump.

-Analysis by Geoffrey Skelley of 538

Christie and Ramaswamy just got into a huge, personal back-and-forth while DeSantis and Haley looked on. Who might voters sympathize with more in that exchange? We can look at each candidate’s net favorability rating for a clue. Ramaswamy has a net favorability rating of +17 points among Republicans, according to 538’s average. That’s not outstanding, but it’s higher than Christie, who is at -34 points. So I’d guess that most Republicans agreed with Ramaswamy more than Christie in that exchange.

-Analysis by Nathaniel Rakich of 538

Christie, pointing his finger at Ramaswamy, said in the first 20 minutes of the debate that Ramaswamy would be voted “the most obnoxious blowhard in America.”

"So shut up for a little while," Christie said.

The former New Jersey governor then offered a defense of Haley, who has so far been the main target of the night.

"He has insulted Nikki Haley's basic intelligence. Not her positions, her basic intelligence," he said, adding, "Look, if you want to disagree on issues, that's fine. Nikki and I disagree on some issues. I've known her for 12 years ... and while we disagree about some issues and we disagree about who should be president of the United States, what we don't disagree on is this is a smart accomplished woman. You should stop insulting her."

Haley turned to Christie and said, “Thank you.”

Ramaswamy went on to criticize both on their foreign policy positions and brought back an attack line he used on Haley at a previous debate: "You can put lipstick on Dick Cheney, it is still a fascist."

-ABC News' Alexandra Hutzler

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