LAS VEGAS — Former Florida Gov. Jeb Bush took several shots at Donald Trump during the Republican presidential debate Tuesday evening.



While on the campaign trail, Trump, the current frontrunner, has repeatedly attacked Bush, taunting him as “low energy.” Bush fired back on stage at the Venetian casino describing Trump as an unserious “chaos candidate.”



“Donald, you’re not going to be able to insult your way to the presidency. That’s not going to happen,” Bush said, provoking loud cheers from the audience.



The back-and-forth between the two candidates began early on when Bush was asked to explain his claim that Trump is “unhinged.” Bush, who was expected to be a major force in the race but has struggled in the polls thus far, stood by his critique of Trump.



“Donald, you know, is great at the one-liners, but he’s a chaos candidate and he’d be a chaos president,” Bush said, adding, “He would not be the commander in chief we need to keep this country safe.”



Trump responded by suggesting Bush only attacked him due to poor poll numbers.



“Jeb doesn’t really believe I’m unhinged,” said Trump. “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.”



Unlike previous debates, on Tuesday Bush held firm, slamming Trump’s proposal to ban Muslim immigrants from entering the country and arguing it would not be effective in the fight against the jihadist group ISIS.



“To be successful in fighting ISIS we need to engage with the Arab world to make this happen. 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,” Bush said, adding, “That’s not a serious proposal. We need a serious leader to deal with this, and I believe I’m that guy.”



The pair fought again when Trump defended his plan to target the family members of ISIS fighters.



Bush dismissed the idea as “troubling” and pointed to comments Trump made in September suggesting America should let Russia take the lead in battling ISIS. He also painted Trump as inexperienced on foreign policy and suggested the frontrunner is getting his policy ideas from television.



“This is another example of the lack of seriousness. Look, this is troubling because we’re at war. They’ve declared war on us and we need to have a serious strategy to destroy ISIS. But the idea that that is a solution to this is just crazy,” Bush said of Trump’s plan to target the families of fighters. The former Florida governor continued, “Two months ago, Donald Trump said that ISIS was not our fight. Just two months ago. He said that Hillary Clinton would be a great negotiator with Iran. And he gets his foreign policy experience from the shows. That is not a serious kind of candidate. We need someone that thinks this through. That can lead our country to safety and security.”



Trump attempted to pivot to immigration and referred to controversial comments Bush made last year that some undocumented immigrants attempt to enter the country to join their families in an “act of love.”



“We need toughness,” Trump said, adding, “I think Jeb is a very nice person. He’s a very nice person, but we need tough people. We need toughness. We need intelligence and we need tough. Jeb said when they come across the southern border they come as an act of love.”



The pair began talking over each other with Bush pointing to Trump’s past statement about Russia and ISIS.



“Am I talking or are you talking, Jeb?” Trump asked.



“I’m talking right now,” Bush retorted. “I’m talking.”



“You’re not talking. You interrupted me,” Trump said. “Are you going to apologize, Jeb? No.”



Bush continued by outlining his strategy for dealing with ISIS and domestic terrorism.



“We need to increase our military spending. We need to deal with the no-fly zone in Syria, a safe zone, we need to focus on building a military that is second to none, so that we can destroy Islamic terrorism,” said Bush.



Trump got the last word of that exchange.



“With Jeb’s attitude, we will never be great again, that I can tell you,” he said.