Source: BBCNews
Republican presidential hopefuls sparred over how to stop the so-called Islamic State (IS), in the first debate since attacks in California and Paris.
The national security focus yielded heated exchanges between Senators Ted Cruz and Marco Rubio who clashed on surveillance and immigration policy.
Jeb Bush also sought to revive his struggling campaign by forcefully attacking front-runner Donald Trump.
"You're not going to be able to insult your way to the presidency," he said.
Mr Trump was on the defensive early in the debate for his proposed ban on Muslims entering the US, saying, "We are not talking about religion, we are talking about security."
However the debate quickly expanded to broader issues of foreign policy and national security.
The candidates repeatedly addressed heightened fears of terrorism in the US on the same day an emailed threat shut down Los Angeles' school system.
The big question going into this last Republican debate of 2015 was how Donald Trump's competitors would try to take the front-runner down.
It seems, however, that only Jeb Bush got that memo. He alone among the candidates engaged the New Yorker directly, and if he had been as forceful several months ago as he was on Tuesday night, his campaign might be in much better shape.
Instead, most of the fireworks during the Las Vegas event occurred between the trio of first-term senators - Marco Rubio, Rand Paul and Ted Cruz.
On the issues of national security and immigration, Mr Rubio faced off against his two congressional colleagues in often acrimonious exchanges.
Barely mentioned over the course of an evening that focused on foreign policy was Mr Trump's call to close the US border to all Muslims.
Given how all the candidates assiduously avoided the subject, one would never have guessed that it was a story that merited global headlines and ignited a firestorm of controversy.
But the top nine candidates disagreed over the scope of government surveillance and how to end the civil war raging in Syria.
"If terrorists strike again... the first question will be, 'Why didn't we know about it and why didn't we stop it?'" said Mr Rubio, taking aim at Mr Cruz, who had voted to curtail government surveillance powers.
Another of Mr Trump's proposals - "closing that internet up" to stop IS recruitment - has been hotly debated, with the candidate saying, "I don't want them using our Internet".
After defending it, he seemed confused by loud booing from the audience, and replied: "These are people that want to kill us folks."
It was not the only time that the crowd played a part in the programme; on several occasions the audience's cheers and jeers forced a pause in the candidates' conversation.
At one point, a heckler interrupted Mr Trump with inaudible comments.