Debates are a test of skill. The skills needed to debate well are specific knowledge and critical thinking.
But since Republicans have made a fetish out of ignorance and the ability to lie on your feet, you can see where they might feel at a disadvantage. Thus, this ultimatum.
The media seem not to be as willing as usual to knuckle under to the GOP insanity. I mean, sure, they're torn between the advertising bucks and their "professional reputations" -- such as they are. They do know how to count and realize how statistically unlikely a Republican president is, but of course they need to hedge their bets.
In other words, business as usual. The Republicans are working the refs to distract their primary voters from the fact that their candidates are a bunch of damned fools. Fortunately, this is not difficult.
Most embarrassing of all? They don't even know how to spell "lightning."
"The Republican Party: Always Marked On The Curve."