Republican presidential candidate retired neurosurgeon Ben Carson gestures as he speaks during the Republican presidential debate in Las Vegas, Dec. 15, 2015. Robyn Beck/AFP/Getty Images

UPDATE 11:15 P.M. EST -- As soon as the debate ended, Twitter was busy sorting out who won the CNN event:

UPDATE 10:50 P.M. EST -- Republican front-runner Donald Trump was asked Tuesday about his remarks that Sen. Ted Cruz had a bad temperament and can't be president. Trump said Cruz was "fine." Then when Cruz was asked about how he feels about Trump, Trump said, "You better not attack me."

Cruz has been reluctant to attack Trump in public, and many pundits have said his respect for Trump is a bare bid to claim Trump's supporters if the business mogul leaves the race. Cruz said Tuesday Trump would be a better president than Barack Obama or Hillary Clinton.

UPDATE 10:32 P.M. EST -- Republican candidates debated immigration Tuesday in Las Vegas, a city with a large Hispanic voting population, and the children of Cuban parents had the most heated exchange. Florida Sen. Marco Rubio said immigrants should eventually be able to apply for work permits, while Sen. Ted Cruz of Texas took a tougher stance. Both men have parents who were born outside the U.S.

UPDATE 10:14 P.M. EST -- A heckler in the crowd during the Republican debate in Las Vegas was escorted out of the theater after he tried to interrupt real estate mogul Donald Trump while speaking. The heckler was shouting about money in politics and the need to remove billionaires like Trump from politics, CNN reporter Dylan Byers said, according to a tweet posted to his verified account.

UPDATE 9:58 P.M. EST -- President George W. Bush once called Islam a religion of peace after the terror attacks of Sept. 11, 2001. Discussing terrorism at the fifth Republican presidential debate Tuesday night, his brother, Jeb Bush, agreed with him.

"We can't dissociate ourselves from peace-loving Muslims," Bush said. "If we expect to do this on our own, we will fail."

Twitter continued to watch the debate ready with puns and quips:

UPDATE 9:40 P.M. EST -- Republican front-runner Donald Trump said during Tuesday's GOP debate hosted by CNN that he was worried about the nation's children being won over by the Islamic State group. Trump said ISIS is “using the internet better than we are using the internet.”

Twitter continued to react to the debate:

UPDATE 9:35 P.M. EST -- Businesswoman and form Hewlett-Packard CEO Carly Fiorina said that the government needed to seek increased participation with the technology sector in fighting terrorism. “They do not need to be forced, they need to be asked to bring the best and brightest to the table,” she said, while adding that governmental surveillance authorities may be using the “wrong algorithm” to find terrorists online.

UPDATE 9:12 P.M. EST --

UPDATE 9:05 P.M. EST --

UPDATE 8:50 p.m. EST -- In his opening statement of the prime-time Republican debate, Kentucky Sen. Rand Paul took the opportunity to attack Donald Trump, comparing his comments about Muslims to North Korea's totalitarian government. "Trump says we ought to close that internet thing," Paul said. "What does he really mean by that? Like they do in North Korea?"

UPDATE 8:37 p.m. EST -- After a fiery undercard debate focused on foreign policy issues, the top-tier Republican presidential candidates began to arrive at the Venetian Theater in Las Vegas, around 8:30 p.m. EST Tuesday. CNN had advertised the prime-time Republican presidential debate as starting at 8:30 p.m., but after the earlier debate began later than expected, people on social media seemed unsure Tuesday when the debate would start.

The opening video for the main debate showed clips of the candidates talking about national security and terrorism interspersed with footage of terror events, all over a track of dramatic music.

Original story:

The Republican debate on Tuesday night in Las Vegas marks the first time GOP candidates will share a stage since deadly terror attacks in Paris and San Bernardino, California, brought national security to the forefront of the political conversation. CNN said ahead of Tuesday that candidates should expect to face foreign policy-related questions during the debate, making it the second showdown this fall to focus on those issues.

Donald Trump, who has continued to lead the polls, was expected to take center stage as he has done in previous debates. CNN said he would be flanked by Texas Sen. Ted Cruz, who has recently shot up in popularity, and retired neurosurgeon Ben Carson, who challenged Trump’s front-runner status last month, but has since faded a bit after fielding criticism over details of his personal history and his foreign policy experience. The other candidates in the prime time event were Florida Sen. Marco Rubio, former Florida Gov. Jeb Bush, Carly Fiorina, New Jersey Gov. Chris Christie, Ohio Gov. John Kasich and Kentucky Sen. Rand Paul.

Tuesday’s debate was important for the Republican candidates because it marked their last chance to take the stage before the end of 2015. With the first primary contests less than two months away, the GOP contenders have been attempting to solidify their images in voters’ minds and were likely hoping to get boosts from strong pre-holiday debate performances.

Some candidates indicated they might use Tuesday’s debate as an opportunity to swipe at Trump. While he remains the clear front-runner in the GOP race, the real estate tycoon has faced intense criticism in recent weeks over his proposal to temporarily ban Muslims from entering the United States. Cruz, who has threatened Trump’s standing in recent Iowa polls, and Rubio, who is known for his foreign policy chops, were also expected to do well.

Earlier in the evening, the four candidates at the bottom of the GOP pack -- former Arkansas Gov. Mike Huckabee, former Pennsylvania Sen. Rick Santorum, South Carolina Sen. Lindsey Graham and former New York Gov. George Pataki -- appeared in an undercard debate. In the last round of debates, Christie had been relegated to this earlier spot, but his poll numbers in New Hampshire were enough to bring him back to the prime time table Tuesday.

Twitter watched the debate and an early undercard debate for low-polling candidates Tuesday: