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At tonight's GOP debate in Las Vegas, it didn't take long for Donald Trump and Jeb Bush to clash over Trump's proposed ban on Muslims entering the U.S.

Bush dismissed Trump's plan as "not serious," saying it would hurt the fight against radical Islamic terror by alienating our Arab allies.

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

Trump countered that Bush doesn't really believe he's unhinged. He asserted that the former Florida governor was just saying that because "he has failed in this campaign."

"It's been a total disaster. Nobody cares."

Watch the exchange above.

UPDATE: On "Fox and Friends," Jeb Bush reacted to his head-to-head clashes with Trump. 

Bush said it's not about liking or disliking Trump, but that the billionaire frontrunner "isn't ready" to be president.

"He's not a serious candidate," said Bush, arguing that Trump's proposed ban on Muslim immigration will make it harder for the U.S. to work with Arab allies against ISIS.

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