Fifth Republican Presidential Debate: 7 Moments That Mattered

Less than 200 miles away from the scene of this month's ISIS-inspired attack in San Bernardino, California, the nine leading Republican presidential candidates used the final presidential debate of the year to loudly beat the drums of war.

At Tuesday night's debate, held in Vegas and hosted by CNN, almost every question focused on national security and the fight against Islamic extremism.

"I began this journey six months ago," frontrunner Donald Trump said. "My total focus was on building up our military, building up our strength."

Meanwhile, Texas Sen. Ted Cruz, rising fast in the polls, doubled down on his call to "carpet bomb ISIS into oblivion," leaving nothing to the imagination: "What it means is using overwhelming air power to utterly and completely destroy ISIS."

Former neurosurgeon Ben Carson declared, "we are at war" while former Florida Gov. Jeb Bush took direct aim at president Obama accusing him of "creating the most unstable situation we've had since the World War II era."

As co-moderator and conservative radio talk show host Hugh Hewitt pointed out, "this will be the debate that Americans talk about at Christmas." Here are seven moments that mattered at Tuesday's presidential debate:

1. Jeb Bush and Donald Trump Spar Over Foreign PolicyRight off the bat, the debate kicked off with a focus on Trump's call to ban Muslims from coming to the United States.

Bush was invited to take the first shot, and started with a fiery quip he surely worked on: "Donald is great at the one-liners. But he's a chaos candidate. And he'd be a chaos president."

But Trump didn't pull any punches. "Jeb doesn't really believe I'm unhinged. He said that very simply because he has failed in this campaign," he responded. "It's been a total disaster. Nobody cares."

Later in the debate, the two were at it again, over battling ISIS.

"Are you talking or am I talking, Jeb?" he asked. "I think Jeb is a very nice person. He's a very nice person, but we need tough people."

But Bush hit back: "Donald, you're not going to be able to insult your way to the presidency. That's not going to happen."

Later, Trump and Bush took the gloves completely off. "The simple fact is if you think this is tough and you are not being treated fairly, imagine what it will be like dealing with Putin," Bush said.

"You're a tough guy, Jeb. I know," Trump said sarcastically, rolling his eyes.

2. Chris Christie Jabs the SenatorsChristie always enjoys digging his rivals on the debate stage who are members of the U.S. Senate, jabbing them and boasting about his executive experience. This evening he had a message for the viewers at home:

"If your eyes are glazing over like mine this is what it is like to be on the floor of the United States Senate," he said. "Endless debates about how many angels on the head of a pin from a person who never had to make a consequential decision in an executive position. For 7 years, I had to make these decisions after 9/11."

Christie continued, stressing he has the experience to keep the country safe adding he worked with Muslims in New Jersey to get intelligence.

"Let's talk about how we do this and not which bill which these guys like more," Christie said. "People don't care about that."

3. Ted Cruz and Marco Rubio TangleOne of the marquee face offs tonight was between Cruz and Rubio, first tussling over the NSA's bulk surveillance program, which expired at the end of last month, and later the defense authorization act, as well as immigration.

"If we continue those cuts that we're doing now, not to mention additional cuts we're going to be left with the smallest and oldest air force this country has ever had and that leaves us less safe," Rubio said, trying to paint Cruz as an isolationist.

Cruz fired back saying "ISIS and radical Islamic terrorism will face no more determined foe than I will be."

"One of the problems with Marco's foreign policy is he is far too often supported Hillary Clinton and Barack Obama undermining governments in the Middle East that have helped radical Islamic terrorists," Cruz continued.

Rubio hit Cruz back saying it sounds like his strategy is "not to lead at all."

Later on the two went at it over immigration with Rubio saying the two of them have a similar position on the issue and Cruz fiercely denying the charge:

"For Marco to suggest our record is the same is like suggesting that the fireman and the arsonist have the same plan because they were at the same fire," Cruz said, stressing he has the more conservative immigration plan.

"We will build a wall that works and I'll get Donald Trump to pay for it," Cruz quipped. Trump got a laugh out of it, saying he would build it.

4. Trump 'Open' to 'Closing' Parts of the InternetTrump reiterated his strategy to cut off ISIS's recruiting methods on social media, which he argues would involve collaboration with Silicon Valley and limiting Internet access.

"I would certainly be open to closing areas where we are at war with somebody," Trump said. "I sure as hell don't want to let people that want to kill us and kill our nation use our Internet. Yes, sir. I am."

Trump later narrowed his answer, clarifying that he was speaking about parts of Syria and Iraq.

The audience then began to boo -- a reaction to his answer Trump was not expecting.

"I just can't imagine somebody booing," he said taken aback. "These are people that want to kill us, folks. And you're objecting to us infiltrating their conversations? I don't think so."

5. Rand Paul Comes Out Of The ShadowsKentucky Sen. Rand Paul barely made the cut for the debate, but he knew how to attract attention -- namely by drawing the ire of Trump.

"I would like to also go back to another question. Which is, is Donald Trump a serious candidate?" Paul asked. "The reason I ask this is, if you are going to close the Internet, realize America what that entails. That entails getting rid of the First Amendment. Okay. No small feat."

He added that some of Trump's proposals for fighting terrorism "would defy every norm that is America."

Paul, who is polling near the bottom of the group of top tier candidates, got an earful from Trump who dismissed his rival's attacks with a wave of his hand.

"These are people that want to kill us, folks," Trump said. "And you're objecting to us infiltrating their conversations? I don't think so. I don't think so."

6. Cruz and Blitzer TussleWhen there are nine candidates on the stage there are going to be times you really want to get in there, but it's not your turn, even if you are the Iowa frontrunner.

CNN moderator Wolf Blitzer was questioning Rand Paul, but Ted Cruz wanted to get into the conversation. Blitzer told him to "hold on" four times, but there was no stopping the Texas Senator.

Cruz kept interrupting with Blitzer telling Cruz to "wait your turn. We have two hours. We'll have plenty of time. "

He didn't stop, saying "the focus should be on defeating our enemies," but Blitzer shut Cruz down two more times before saying, "These are the rules you all agreed to."

7. Trump Promises Not to Run as an Independent...AgainIt's a pledge we've heard before, but tonight Trump again said he wouldn't run as an independent.

Moderator and conservative talk radio host Hugh Hewitt asked the reality television star to "assure the people that you will run as a Republican?" Trump answered concisely: "I really am."

In September, Trump signed a pledge to not run as an independent, but since then he has said he was still considering the option.

"I've gained great respect for the Republican leadership," Trump explained. "I've gained great respect for many -- in different forms for the people on the dais. I have great respect for the people I have met in this process. But I will tell you, I am totally committed to the Republican party. I feel very honored to be the frontrunner."