Nine leading Republican presidential contenders clashed over national security issues Tuesday in a debate highlighted by several feisty exchanges between top tier candidates.
The debate in Las Vegas, Nevada, took place with less than two months before the Iowa caucuses - the crucial, first nominating event of the primary election season.
The early part of the debate focused on frontrunner Donald Trump's call to temporarily ban Muslims from entering the United States, following several recent terrorist attacks.
The reality television star and real estate developer defended the proposal as common sense, insisting "we are not talking about religion, we are talking about security."
"People like what I say. People respect what I say. And we've opened up a very big discussion that needed to be opened up," Trump said.
Though many Republican leaders have criticized Trump's Muslim ban, most candidates on Tuesday appeared reluctant to directly confront Trump on the issue.
Jeb Bush speaks during the CNN Republican presidential debate at the Venetian Hotel & Casino on Tuesday, Dec. 15, 2015.
Former Florida Governor Jeb Bush instead attacked Trump's flamboyant style, saying he is "great at one-liners, but he's a chaos candidate and he'd be a chaos president."
Throughout the evening, Bush and Trump engaged in several heated exchanges, often talking over one another in an attempt to gain the upper hand.
"You're never going to be president of the United States by insulting your way to the presidency," said Bush, who was once seen as a frontrunner, but whose campaign has struggled to gain momentum.
"Well, let's see. I'm at 42 [percent], and you're at three [percent]. So, so far, I'm doing better," Trump said, apparently referring to his standing in a recent poll.
Bush also portrayed himself as more knowledgeable on policy issues, mocking Trump, who once said he gets military advice from watching television shows.
"I won't get my information from the shows," said Bush, who questioned whether Trump was getting his information from Sunday morning news shows or Saturday morning cartoons.
Trump rules out independent run
Despite widely being seen as a poor performer during the five Republican debates, Trump has opened up a massive lead in most national opinion polls.
Trump's success even as the primary elections draw closer has rattled many in the GOP establishment, who are concerned he may either win the nomination or mount a third party presidential bid.
Donald Trump, center, speaks as Ben Carson, left, and Ted Cruz look on during the CNN Republican presidential debate at the Venetian Hotel & Casino on Dec. 15, 2015, in Las Vegas.
When asked by a debate moderator Tuesday whether he is ready to commit to not running as an independent if he does not win the Republican nomination, Trump replied: "I'll be honest. I really am."
Trump in September held a press conference to rule out a third party run, but has since said he will reconsider if he feels he is not treated fairly by other Republicans.
Cruz focus on Obama
In recent weeks, Texas Senator Ted Cruz has emerged as one of Trump's main challengers, especially in Iowa, where many polls even place him in the lead over Trump.
Cruz has famously refused to publicly criticize his rival, and on Tuesday directed his ire against President Barack Obama and his military campaign against the Islamic State group.
The Texas senator accused Obama of waging a "photo opp" war against Islamic State. He again repeated his threat to "carpet bomb" extremists in Iraq and Syria.
"If elected, we will hunt down and kill the terrorists," Cruz said. "We will utterly destroy ISIS. We will stop the terrorist attacks before they occur because we will not be politically correct."
Ted Cruz, right, makes a point as Donald Trump reacts during the CNN Republican presidential debate at the Venetian Hotel & Casino on Dec. 15, 2015, in Las Vegas.
For much of the night, Cruz engaged Florida Senator Marco Rubio in lengthy debates over issues including what to do about Islamic State, domestic surveillance programs, and immigration.
One notable moment was when the two senators discussed a recently suspended National Security Agency program to collect bulk phone records of American citizens.
"We are now at a time when we need more tools, not less tools," Rubio said in defense of the program. "And that tool we lost, the metadata program, was a valuable tool that we no longer have at our disposal."
Cruz, who voted against the program, shot back, saying that NSA surveillance is now stronger than it was before. "Marco knows what he's saying isn't true," Cruz said.
Cruz and Rubio, both Cuban Americans in their 40s, have shot up in recent national polls. According to the latest Wall Street Journal/NBC News poll, Trump was at 27 percent, followed by Cruz with 22 percent. Rubio came in third with 15 percent.
The other candidates in Tuesday's debate were ex-Hewlett Packard CEO Carly Fiorina, Ohio Governor John Kasich, retired neurosurgeon Ben Carson, New Jersey Governor Chris Christie, and Kentucky Senator Rand Paul.
Earlier, a pre-debate forum featured four other candidates: former Pennsylvania senator Rick Santorum, former Arkansas governor Mike Huckabee, South Carolina Senator Lindsey Graham and former New York governor George Pataki. Those four did not qualify for the main event.