CNN/screenshot
Donald Trump, left, and Jeb Bush at the CNN debate.
After Bush called Trump a "chaos candidate" earlier in the debate, another back-and-forth began with a question for Trump about his statement that he would go after the families of ISIS terrorists.
Trump reaffirmed his previous statement, saying: "I would be very, very firm with families, and frankly, that will make people think because they might not care much about their lives, but they do care, believe it or not, about their families lives."
Bush then jumped in, saying: "This is another example of the lack of seriousness" of Trump's candidacy.
He then said that ISIS has declared war on the US, emphasizing the need to have a "serious strategy" to destroy ISIS.
"The idea that that is a solution to this is just crazy," Bush said. "It makes no sense to suggest this."
Bush then pointed out that two months ago, Trump said that ISIS was "not our fight." Trump then cut in to say he never said that. (It was actually one month ago that Trump told CNN in an interview that the conflicts in the Middle East were "not our fight.")
"He gets his foreign policy experience from the shows," Bush said.
"Aw, come on," Trump responded, shaking his head.
Bush continued, "That's not a serious kind of candidate. We need someone that thinks this through, that can lead our country."
Trump then implied that Bush is weak.
"We need toughness," Bush said. "I think that Jeb is a very nice person … but we need tough people. We need toughness."
Bush cut back in, and then the two talked over each other.
"Am I talking or are you talking, Jeb?" Trump said, to which Bush replied: "I'm talking right now."
"I know you're trying to build up your energy, Jeb, but it's not working very well," Trump fired back.
"We need a toughness, we need strength," Trump added. "We're not respected as a nation anymore, we don't have that level of respect that we need, and if we don't get it back fast, we're just going to go weaker, weaker, and just disintegrate. ... We need strength; we don't have it."
But Bush didn't back down.
"Donald, you're not going to be able to insult your way to the presidency. That's not going to happen," he said. "And I do have the strength. Leadership is not about attacking people and disparaging people."
Trump closed the back-and-forth with this zinger: "With Jeb's attitude, we will never be great again, that I can tell you. We will never be great again."