Obama was always a poor debater, so the only surprise in last week's match-up was Romney's gusto.
Obama is a poor debater because he does not stand for anything. He is essentially a servant of Wall Street hiding in cliché liberal rhetoric. He is moderator-in-chief.
He can not respond to critics from the left, because he wants to believe he is on their side but would have to admit they are right, that he is not at all on their side.
And he can not respond to critics from the right, because he would have to show that they are wrong, which he can not do, because he needs his liberal supporters to believe he is on their side.
Poor man: how to reassure the fascists as well as the vestigial liberals.
And any challenger can easily upset his delicate balancing act by upping the ante, forcing him to defend one or the other, to take on the role of conservative or liberal in the charade of U.S. elections. The incumbent wants to remain neither, throwing rhetorical and occasional executive sops to one constituency or another, and the challenger, if victorious, will become neither in the same way (and in turn challenged in the same way). Thus we are asked to choose between Coke and Pepsi, and those that would choose neither (thinking a cup of tea, perhaps, or glass of seltzer would better serve) are ostracized, clearing the field for this mock politics.
Update, Oct. 18: When Romney tells you that Obama's responses to the Bush recession didn't help middle class families, he should be asked how his family fared. But that would reveal that Obama has done very well by Romney, which neither of them want to publicize.