GOP-2016-Debate_Byun5-1024x674The growing terror threat exposed fault lines in the Republican primary field as the leading candidates sparred sharply at Tuesday’s debate over who is best equipped to confront the Islamic State.

Most candidates on stage at the final primary debate of the year scrambled to sound the toughest message against the terror group.

“We will utterly destroy ISIS,” Texas Sen. Ted Cruz vowed, later adding: “ISIS and radical Islamic terrorism will face no more determined foe than I will be.”

Though Cruz is catching up to Donald Trump in the polls – and surpassing him in Iowa – the billionaire businessman continued to draw a lot of the fire from his primary rivals on stage. Trump personally defended his controversial plan to ban Muslims from entering the United States in the face of tough criticism from other Republican candidates, particularly Jeb Bush.

Bush, after a string a debates that saw him fading from the forefront of the race, stepped up his attacks on Trump, and called his plan “not a serious proposal.”

“He’s a chaos candidate, and he’d be a chaos president,” Bush said.

Trump fired back that “Jeb doesn’t really believe I’m unhinged” and only went after him because he’s “failed in this campaign.”

Cruz and Sen. Marco Rubio also sparred over some of Cruz’ Senate positions – including for legislation reining in NSA metadata collection. Rubio accused Cruz of helping take away a “valuable tool” for security officials, while Cruz said: “Marco knows what he’s saying isn’t true.”

New Jersey Gov. Chris Christie used the arguing to contrast his own executive experience against senators’ legislative history. He described their jobs as “endless debates about how many angels on the head of a pin from people who have never had to make a consequential decision.”

The leading GOP candidates focused on the terror threat throughout the CNN-hosted primary debate Tuesday night in Las Vegas – an event held just hours after Los Angeles closed its school system over a terror threat.

Citing that closure, which is now thought to have been prompted by a hoax threat, Christie also said children will be going back to school filled with anxiety. And he said the country’s overall security environment has been hurt by President Obama and Hillary Clinton’s policies.

“America has been betrayed,” he said.

The prime-time debate in Las Vegas comes at a time of shifting dynamics in the campaign. While Trump maintains his lead in most national polls, Cruz has surged to the front of the pack in the crucial state of Iowa.

Cruz’ ascent in the polls already has started to stir tensions between the two candidates, who until now have steered clear of directly criticizing one another.

Trump said over the weekend that Cruz acts on Capitol Hill “like a bit of a maniac.” Cruz has since teased him over the jab.

Ben Carson, meanwhile, has seen his numbers steadily fall while Florida Sen. Marco Rubio is holding at around third position in most surveys.

All candidates have tried to refocus on security after the San Bernardino terror attack that left 14 dead, and the Paris terror attack last month.

Unlike the most recent GOP debate, this time Christie is back on the prime-time stage after seeing an uptick in polling and qualifying for the main event.

CNN also hosted a debate Tuesday for the second-tier GOP candidates — former Arkansas Gov. Mike Huckabee, former Pennsylvania Sen. Rick Santorum, South Carolina Sen. Lindsey Graham and former New York Gov. George Pataki. Graham was particularly critical of Trump’s Muslim ban plan at that debate, accusing him of declaring war on Islam and delivering a “coup” for ISIS.