That probably wasn't a joke. He's never had to do this for 90 minutes straight before. They're worried he might lose it even worse than normal due to the pressure of having to be out there that long. Compare that to Clinton, who sat through an 11 hour Benghazi hearing, and the image alone would do a ton of damage.
Exactly, if they haven't housebroken him then no matter what he has memorized or written on his palms he's going to be a national embarrassment. There's also no doubt that Hillary can play the immovable object and weather anything they throw at her, but...
Well yes but she has been waiting to debate legit Republicans, not a pathological liar who is borderline fascist and built an entire campaign based on being a complete asshole and breaking the rules every step of the way.
That's an issue too; Trump is the proverbial unstoppable force and that kind of raw unpredictable energy might just be enough to throw her off the game, not because he can out-debate her but because it's not going to be a real debate at all. It'd be like putting Muhammad Ali in the ring against a guy in a mascot costume; yeah, Hillary knows how to debate Republicans, but how do you debate something hollow that dances around flailing, playing to the crowd and doesn't even know how or try to throw a punch?
It ends up making the the whole thing look like a farce (which, let's be real, it is just by virtue of having Trump on the stage at all) and runs the risk of making her look like the straight man to his zany antics. It might throw her off just enough that she gaffes (which, let's face it, if she gaffes
once, even slightly, that's all that will be replayed the next morning).
I don't know, Trump is basically the manifestation of the GOP machine that has been beating on Clinton for decades. A misogynistic, lying, conspiracy theorist backed by Citizens United, Breitbart, and Roger Ailes.
Those last two are political operatives who, as despicable as they are, know how to do their jobs. Trump is a
literally a television game show host. He's not the manifestation of any great Republican political power, he's just a carnival barker who saw everyone else was dumping their gasoline and was shrewd enough to bring matches.