CNN is stressing that unlike Fox News, its first Republican presidential primary debate will be open to all the GOP candidates.

On Monday, the Wall Street Journal published a letter from CNN Washington Bureau Chief Sam Feist, who explained that the network is having one debate that will be divided into two back-to-back segments.

"CNN is not limiting the participants in our debate … rather CNN will produce a debate that is as inclusive as possible," Feist wrote. "When CNN and the Ronald Reagan Presidential Library announced our Sept. 16 debate, we stated that any Republican candidate polling at or above 1 percent in national polls would be invited to the debate. We expect between 15 and as many as 17 candidates to receive invitations."

CNN plans to reserve one segment of its debate for the candidates that haven't cracked the top 10, while the other segment immediately following would feature only those candidates who are polling in the top 10 of an average of national surveys.

The format would likely benefit the so-called "second-tier" candidates whose poll numbers could get a boost from a strong national debate performance. (CNN did not return a request for comment on whether both segments will be equal in duration.)

By contrast, Fox News is hosting a two-hour primetime debate several weeks ahead of CNN, the first of the campaign, and it will include only the candidates who poll nationally in the top 10. The other candidates will be given an hour-long "forum" to participate in four hours earlier, at 5 p.m. ET. Because of the gap between the "forum" and the debate, there will likely be a significant discrepancy in viewership.

Fox has so far released few details about the nature of its "forum" and did not return a request for comment on how it will differ from the network's debate.

In May, when Fox announced its debate plans, critics charged that it rewarded name recognition and celebrity status. Some say polls in early primary states are more important than national ones, and that this should be a factor.

Fox anchor Bret Baier, who is co-moderating the network's debate, recently suggested that a future debate hosted by Fox may use different criteria in determining which candidates make it on stage.

In an op-ed Sunday for the Wall Street Journal, Republican National Committee spokesman Sean Spicer defended the debate schedule sanctioned by the RNC as the "most inclusive setup in history."