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

“Father time is undefeated,” DeSantis told the debate audience twice, raising doubts over Trump’s age, at 77 years old, amid intervening attacks from Christie that he avoided the original question.

“He’s afraid to answer … this is the problem with my three colleagues,” Christie said. “They’re afraid to offend.” DeSantis wouldn’t respond to repeated questions by Christie and the moderators on the former president’s fitness for office.

“I’ll concede you’re fit, Ron,” Christie said. “You’re a new generation.”

- ABC News’ Chris Boccia

Addressing Trump's comments in an interview on Tuesday referring to himself as a "dictator" but only on "Day 1," Christie called the former president an "angry, bitter man who now wants to be back as president because he wants to exact retribution on anyone who has disagreed with him."

"Do I think he was kidding when he said was a dictator? All you have to do is look at the history," he said. "That's why failing to speak out against him, making excuses for him, pretending that somehow he's a victim empowers him."

Christie -- who Trump has dismissed as a failure both as a governor and candidate -- charged that the other hopefuls on stage "make it seem like his conduct is acceptable" because they said they would still support him if he was convicted of federal felonies, which Trump denies.

"Let me make it clear: His conduct is unacceptable," Christie said. "He's unfit."

Christie warned to "be careful of what you'll get."

"He will only be his own retribution. He doesn't care for the American people. It is Donald Trump first," he said, eliciting some boos from the crowd.

-ABC News' Meredith Deliso

Banking experts told PolitiFact that DeSantis’ claim about President Joe Biden pushing a “central bank digital currency” was dubious. Even if the system were technically feasible, current U.S. laws would not permit the kinds of monetary surveillance and control that DeSantis described, they told PolitiFact in April. The Federal Reserve is studying the possibility of creating a digital currency. But DeSantis’ remarks overstate the likelihood that such a system is possible, much less likely, to emerge in the United States -- for a variety of technical, legal and political reasons, experts told us.

-Analysis by Katie Sanders of PolitiFact

Asked what threats she worries could blindside the U.S. amid what federal officials have called a heightened threat level during the Israel-Hamas war, Haley focused on "foreign infiltration."

"America right now is acting like it's Sept. 10. We better remember what Sept. 12 felt like, because it only takes one," she said.

"We've got to get the foreign infiltration out of our country -- whether it's in our schools, whether it's on our social media, we need to stop all foreign lobbying that's happening to members of Congress, and we need to start securing America again," she continued.

-ABC News' Meredith Deliso