In Tuesday night's main debate, former Florida Gov. Jeb Bush attacked billionaire front-runner Donald Trump's proposal to temporarily block all foreign Muslims from entering the United States.
"This is not a serious proposal. In fact, it will push the Muslim world, the Arab world, away from us," Bush said, after prompting from CNN moderator Wolf Blitzer. "Donald is great at the one-liners. But he's a chaos candidate. And he'd be a chaos president."
Trump, who seemed uncharacteristically low-key, responded by insulting Bush. "He said that very simply because he has failed," Trump said. "Nobody cares" about Bush.
Sen. Ted Cruz of Texas, newly ensconced in second place, seemed to want to play both sides of the fight. Cruz said he understood Trump's motivations: "Everyone understands why Donald has suggested what he has."
But Cruz said that Trump's proposal was too broadly drawn, and that Cruz himself did not want to block all Muslims.
'It's not a war on a faith," said Cruz, who earlier had said "America is at war. "It's a war on a political and theocratic ideology that seeks to murder us."
The debate could be a crucial showcase for Cruz, who has risen in the race as retired neurosurgeon Ben Carson has faded. Cruz has already taken criticism from Trump and from the fourth major contender in the race, Sen. Marco Rubio of Florida.
At the start of the evening, Sen. Rand Paul of Kentucky, the lowest-polling candidate on the main stage, began with an attack on Trump and Rubio for what he called an overreaction to the terrorist attacks. Rubio, he said, had called for increased government data collection.
"I think they're both wrong," Rubio said. "I think we defeat terrorism by showing that we do not fear them."
But that voice of skepticism about terrorism fears was quickly lost when New Jersey Gov. Chris Christie mentioned a bomb scare that shut down Los Angeles' enormous school system on Tuesday. The threat had been determined to be a hoax, but Christie still used it as evidence that the country was less safe under President Barack Obama.