What You Need to Know for the Republican Debate

Nine Republican presidential candidates will line up across the prime-time stage Tuesday night for their fifth and final debate of 2015, as front-runner Donald Trump continues to dominate both national headlines and the polls.

Five of the nine candidates—real estate mogul Trump, Texas Senator Ted Cruz, retired neurosurgeon Ben Carson, Florida Senator Marco Rubio and former Florida Governor Jeb Bush—received more than the 3.5 percent average needed in the national polls. Candidates qualified if they earned an average of 3.5 percent in the polls conducted nationally between October 29 and December 13, or 4 percent in either Iowa or New Hampshire, two early primary states.

Since co-host CNN also accepted the 4 percent polling average in Iowa and New Hampshire, New Jersey Governor Chris Christie, Ohio Governor John Kasich, former businesswoman Carly Fiorina and Kentucky Senator Rand Paul will accompany the others on the main stage. The event begins at 8:30 p.m. ET, 5:30 p.m. PT, from The Venetian in Las Vegas.

The debate, also hosted by the Salem Radio Network, is one of the last two Republican matchups before the Iowa caucuses on February 1. The Hawkeye State is significant for campaigns because it holds the first major electoral event of the presidential nominating process.

Christie, whose polling numbers recently have been on the rise in New Hampshire, returns to the main stage after being in the undercard in the last debate. CNN seemingly tweaked its criteria to add Paul at the ninth podium.

An earlier so-called "undercard" debate will include four of the candidates who aren't polling as well as the other nine—former Arkansas Governor Mike Huckabee, South Carolina Senator Lindsey Graham, former Pennsylvania Senator Rick Santorum and former New York Governor George Pataki. That debate will begin at 6 p.m. ET, 3 p.m. PT.

The other GOP candidate, former Virginia Governor Jim Gilmore, didn't poll high enough to earn a spot on either stage.

As they have done in the four previous debates, the candidates are expected to continue to try to figure out how to diminish Trump who will take center stage, with Carson on his right and Cruz on his left. As Carson's popularity has declined in the past month, Cruz now polls first in Iowa.

This debate comes following Trump's proposal to ban temporarily all Muslims from entering the U.S., in the wake of the deadly shooting earlier this month in San Bernardino, California. The event elevated national security and terrorism as a main issue on the campaign trail.

CNN's Wolf Blitzer and Dana Bash, along with Salem Radio's Hugh Hewitt, will moderate. Viewers can livestream the debate for free at CNN.com.

Louisiana Governor Bobby Jindal dropped out of the GOP race for the White House just days after the last debate on November 10. Wisconsin Governor Scott Walker and former Texas Governor Rick Perry also abandoned their bids for the presidency.