Celebrity billionaire Donald Trump came under fire for his controversial proposal to ban Muslims from entering the United States, on a night when terrorism clearly became the centrepiece issue of the presidential campaign.
Tuesday night's Republican presidential debate was the party's first since the terrorists attacks in Paris and California, and security thus dominated the two-hour event.
The serious nature of the issue appeared to play to the strengths of establishment Republicans, as candidates such as ex-Florida governor Jeb Bush and New Jersey Governor Chris Christie - for so long overshadowed in this campaign - finally had good outings on the debate stage.
Mr Bush's best moments all came during his multiple exchanges with Mr Trump, with the former governor portraying himself repeatedly as the grown-up in the room, while simultaneously painting the businessman, who is nicknamed the Donald, as irresponsible.
He led the attacks from nearly all the candidates on stage against Mr Trump's proposed Muslim ban.
STICKS AND STONES...
Donald, you're not going to be able to insult your way to the presidency. That's not going to happen.
FORMER FLORIDA GOVERNOR JEB BUSH, frequently derided by rival Donald Trump as lacking vim, hits back in a personal fashion of his own
A CHAOS PRESIDENT
Donald is great at the one-liners, but he's a chaos candidate. And he'd be a chaos president... He would not be the commander in chief we need to keep our country safe.
MR JEB BUSH
If I'm elected president, we will secure the border. We will triple the border patrol. We will build a wall that works - and I'll get Donald Trump to pay for it.
TEXAS SENATOR TED CRUZ, taking a jab at billionaire Trump's bulging bank account
"This is not a serious proposal," said Mr Bush. "In fact, it will push the Muslim world, the Arab world, away from us at a time when we need to re-engage with them to be able to create a strategy to destroy ISIS (Islamic State in Iraq and Syria).
"Donald is great at the one-liners, but he is a chaos candidate. And he would be a chaos president."
Mr Christie, meanwhile, successfully emphasised his credentials as a straight-talker and an effective pragmatist, by constantly returning to his experience as a former federal prosecutor in the aftermath of the Sept 11, 2001, terror attacks.
Mr Trump, in turn, had a rare night where he was overshadowed by others and occasionally seemed out of depth discussing ISIS strategy or foreign policy.
His one standout remark came late, when he pledged to abandon the possibility of a third-party run and commit to the Republican Party. He had turned his back on such a pledge before, but his language this time was the clearest yet.
Asked if he was ready to assure Republicans that he would run as a Republican, Mr Trump said: "I really am. I will be honest, I really am."
And while many had anticipated a showdown between Mr Trump and Mr Ted Cruz, who has surged in the polls, it did not materialise.
Though the Texas senator disagreed with Mr Trump's Muslim ban, the two men declined to repeat the attacks they had launched at each other ahead of the debate.
Mr Trump walked back remarks he made at the weekend, where he called Mr Cruz a maniac, and Mr Cruz evaded questions about a private meeting where he raised doubts about Mr Trump's judgment.
Mr Cruz, currently behind Mr Trump in Iowa, did, however, engage in lengthy policy exchanges with Florida Senator Marco Rubio.
The two Cuban-Americans thus provided the most substantial parts of the debate, clashing over the need for the National Security Agency's bulk phone data collection scheme and whether or not illegal immigrants in the United States should be legalised. Mr Rubio supports a path to legalisation, while Mr Cruz does not.
The rest of the field had largely forgettable nights. Retired neurosurgeon Ben Carson has fallen significantly in the polls since the last debate, and his poor grasp of foreign policy was again evident.
Still, experts say there were no major victories or defeats as a whole and do not see any major reshuffling in the polls. Though Mr Bush and Mr Christie had good nights, most question if it came too late in the game.
"Governor Jeb Bush turned in his best performance to date and had Trump on the ropes for a good period of time. He was the only candidate willing to tussle with the front runner and got the better of several early exchanges," said University of Michigan director of debate Aaron Kall, who expects Mr Trump to maintain his lead.
One more Republican debate remains before the first votes for the nominee are cast in Iowa on Feb 1.