You've got it. There is a LOT of intimidation in that little word.
Obama is scouring his memory about now, trying to remember anything that could bring him down - or, he knows what it is and the game is over for him, if he doesn't want it revealed.
The other possibility is that he could call her on it, and try to turn the tables on her.
I am willing to bet he had an inkling or two before the debate.....he was not in the game for that last one, this would explain it.