Republican front-runner Donald Trump and former Florida governor Jeb Bush locked horns in a national security debate in Las Vegas Tuesday evening, leading the former Florida governor to say the real estate mogul is little more than a "chaos candidate" who can't simply "insult [his] way to the presidency."

It was the first time that any of the Republican candidates stood up to the signature attack deployed by Trump, who has routinely attempted to denigrate his opponents with insults based on their appearance, lack of wealth or low polling numbers.

"Donald, you’re not going to be able to insult your way to the presidency. That’s not going to happen," CNN reported Bush as saying. "And I do have the strength. Leadership, leadership is not about attacking people and disparaging people. Leadership is about creating a serious strategy to deal with the threat of our time."

When asked about comments he made about Trump being "unhinged," Bush said, "Donald, you know, is great at the one-liners, but he’s a chaos candidate and he’d be a chaos president," Reuters reported.

However, Trump replied that Bush was motivated to attack because of his low polling, according to Yahoo!.

"Jeb doesn’t really believe I’m unhinged," Trump said. "He said that very simply because he has failed in this campaign. It’s been a total disaster. Nobody cares and, frankly, I’m the most solid person up here. I built a tremendous company."

Bush hit Trump on his proposal to temporarily ban all Muslims from entering the United States and the impact that would have on the country's efforts to defeat ISIS.

"We need to engage with the Arab world to make this happen," said Bush, according to the debate transcript published by The New York Times. "It is not a serious proposal to say that - to the people that you’re asking for their support that they can’t even come to the country to even engage in a dialogue with us. That’s not a serious proposal. We need a serious leader to deal with this. And I believe I’m that guy."