This debate (the fifth for the GOP) will feature nine candidates on the primetime stage. Just five of those nine managed to qualify by topping 3.5 percent in an average of national polls — Donald Trump, Ted Cruz, Marco Rubio, Ben Carson, and Jeb Bush. However, CNN also took polling averages in Iowa and New Hampshire into account, so Chris Christie, John Kasich, Carly Fiorina, and Rand Paul also made the cut (though CNN had to bend its rules a bit to get Paul in).
Four other candidates — Mike Huckabee, Lindsey Graham, Rick Santorum, and George Pataki — will be relegated to the earlier undercard debate. The other GOP candidate still running, Jim Gilmore, failed to qualify.
What to expect at the CNN Republican debate
As ever, Donald Trump will remain the center of attention. With just a month and a half more until voting starts, the once unthinkable prospect that Trump could actually win early states is looking increasingly less unthinkable — he's still leading polls both nationally and in New Hampshire, and his rivals remain at a loss about how to dislodge him.
But expect more of a focus on Ted Cruz than ever before. In the month since the last GOP debate, the Texas senator has surged to first place in Iowa and second place nationally, benefiting from the decline of Ben Carson. Cruz is an outsider candidate loathed by the establishment, but he also has some conventional credentials and political experience. As such, he's become a serious threat to both the outsider Trump and the more conventional Marco Rubio (who has fallen behind Cruz in polls for the first time in months).
So in the past few days, both Trump and Rubio have begun to attack Cruz. Trump has suggested that Cruz is a tool of Big Oil, that he lacks the judgment to be president, and that he's been "a little bit of a maniac" in the Senate. Meanwhile, Rubio has tried to claim that Cruz's support of surveillance reforms makes him weak on national security. But they might be more cautious about attacking Cruz on Tuesday night, because the Texas senator is a skilled and savvy debater.
Beyond these main events of Trump versus Cruz and Rubio versus Cruz, another interesting subplot is the battle for New Hampshire. Though national polls suggest Rubio is the last GOP establishment candidate standing, he hasn't particularly impressed in the Granite State. And three other candidates who are behind Rubio nationally — Christie, Bush, and Kasich — all remain in the hunt there. Those three desperately need a New Hampshire win to get back in the national spotlight, so expect their pitches to be aimed squarely at the state's voters.
How to watch:
When: 8:30 pm Eastern tonight (is when "coverage begins," actual debate probably starts around 9 pm)
Where: The Venetian Las Vegas
Online: At CNN.com, a free live stream will be available
Update: Clarified that CNN is being vague about when "coverage" of the debate will begin vs. the debate itself.