The stakes were high at the last Republican debate of the year, hosted by CNN in Las Vegas Tuesday night, as candidates traded blows in a crowded GOP field. The first primaries are slated to take place in February and candidates were eager to showcase their knowledge on national security and terror threats before voters took to the polls for the first time in 2016.

Real estate mogul Donald Trump remained in the lead, with an average of 33 percent voter support, according to Real Clear Politics, leading the pack by more than 16 percentage points. The theme of Tuesday’s debate was how best to defend the nation against a growing terror threat.

The fear of terrorism has been high in recent months, following a spate of terror attacks in Paris that left 130 dead in November as well as an Islamic State group-inspired attack in San Bernardino, California, that left 14 dead Dec. 2. Amid the rising threat of Islamic extremism, the candidates looked to lay out their plans for protecting the nation.

Here's a round-up of some of the best moments of Tuesday night's debate -- the great call-outs between candidates, the best questions, the memorable foreign policy analyses.

When asked what he thought of Trump's proposal to ban all Muslims, former Pennsylvania Sen. Rick Santorum said during an early debate for low-polling candidates that though he disagreed with the plan itself, more monitoring for people entering the country needed to be put in place. “The fact is, not all Muslims are jihadists. But the reality is, all jihadists are Muslims,” Santorum said.

Sen. Lindsey Graham of South Carolina slammed Trump's proposal for a ban on all Muslims entering the country while noting the number of Muslim-Americans who serve in the U.S. armed forces.

Graham advocated fighting ISIS by pushing them offline, cutting off their recruitment channels through social media.

Former Arkansas Gov. Mike Huckabee said that surveillance of mosques would not violate any constitutional rights. "If Islam is as wonderful and peaceful as its adherents say, shouldn’t they be begging us to come in and listen to these peaceful sermons... so that we all would convert to Islam?" he asked.

Kentucky Sen. Rand Paul and Florida Sen. Marco Rubio went head-to-head on immigration policy. 

Trump took aim at Florida Gov. Jeb Bush, saying that nobody cared what he thought.

The candidates offered their solutions to fighing terrorism online, with Texas Sen. Ted Cruz arguing for more metadata collection and businesswoman Carly Fiorina saying that governmental organizations needed to seek heightened coordination with the technology sector.