Trump defends Muslim policy, Bush calls him 'chaos candidate'

Not surprisingly, Republican front-runner Donald Trump's controversial proposal to ban non-citizen Muslims from entering the United States led off Tuesday's GOP debate in Las Vegas.

Trump, of course, defended the plan saying it wasn't about religion. "“We’re talking about security," he said.

His longtime nemesis, Jeb Bush, went on the attack.

“This is not a serious proposal," the former Florida governor said, explaining that it would drive away Arab allies.

“Donald is great at the one liners," Bush said. "But he’s a chaos candidate. And he’d be a chaos president.”

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Trump fired back against Bush's previous claim that he was "unhinged."

“Jeb doesn’t really believe I’m unhinged," Trump said. "He said that very simply because he’s failed in this campaign.

Marco Rubio and Ted Cruz, meanwhile, largely stayed away from aggressive hits against Trump's proposal. Cruz, who's emerged as the New York billionaire's chief rival in Iowa, said he understood why Trump came up with the plan.

“I’m reminded of what FDR’s grandfather said," the Texas senator explained. "He said, 'All horse thieves are Democrats, but not all Democrats are horse thieves,” adding that there are "millions of peaceful Muslims" across the globe.