With the lead-off nominating contests starting in less than a month, it’s fast becoming clear which candidates have a credible shot at winning the Republicans’ presidential nomination and, perhaps more tellingly, which do not.

Sen. Rand Paul of Kentucky and former tech executive Carly Fiorina were bumped from the primetime lineup, and Paul says he’s skipping the earlier undercard debate. Fiorina will face former Arkansas Gov. Mike Huckabee and former Sen. Rick Santorum of Pennsylvania, two darlings of Christian conservatives.

Remaining on the main stage are frontrunner Donald Trump, Sen. Ted Cruz of Texas, Sen. Marco Rubio of Florida, retired neurosurgeon Ben Carson, New Jersey Gov. Chris Christie, former Florida Gov. Jeb Bush and Ohio Gov. John Kasich.

With Iowa having the first nominating contests on Feb. 1, the dynamics of the race are incredibly fluid and the candidates’ attacks are getting sharper. Cruz, who for months refused to tangle with Trump, has started to get tougher with the brash billionaire. The animosity between Bush and Rubio has reached peak rivalry, so much so that advisers wonder if their onetime close relationship is beyond repair.

And the attacks on Christie are starting to grate him as he is working to beat expectations in Iowa and meet them in New Hampshire.

The debates have so far drawn record number of viewers as interest in the ever-dramatic GOP race builds. The debates—as much as the polls that determine who gets the best seats on stage—have been touchstones for the campaign and many national donors have taken the measure of the race by the televised food fights.

At this moment in the campaign, the biggest question for Republicans is what happens in Iowa. Will the thrice-married Trump keep his advantage in a state ripe with Evangelicals, or will Cruz be able to claim the top spot? Trump’s unconventional campaign is betting his reality star approach can sustain him against Cruz, who has done three times as many events as Trump. If Trump falters in Iowa, can he catch himself in New Hampshire, or will he fade? And will any of it matter for his legions of supporters?

To help offset his slide, Trump has turned to questions about Cruz’s eligibility to even serve as President. Cruz was born in Canada to an American mother, and Trump has suggested that Cruz might be tempting challenges over whether he is a “natural-born citizen” as the Constitution demands.

Legal scholars of both parties have said that Cruz is fine, but that’s seldom enough for Trump the provocateur and Cruz advisers are starting to take note of the furor over his eligibility that has consumed conservative media. Viewers should brace for a prickly Cruz response.

The Fox Business Network debates begin at 6 p.m. for the lower-polling candidates. The better-faring candidates meet at 9 p.m.

This article was originally published on Time.com.