Andrew Sullivan puts the debate in perspective:
Now I've slept on it, that seems to me what happened last night. It was such a mesmerizing sales job and so relentless, checked at no point by Lehrer, and at no point checked by past reality or facts, Obama was left with two options: say this pleasant-seeming guy next to him is a shameless weather-vane and liar (wouldn't work in a debate, is just against Obama's character) or to try and remind the country of Romney's actual policies as he has laid them out, and rebut the facts relentlessly. Obama tried the latter really, really badly, but the obvious retort to Romney's smiling total pivot was: what on earth are you talking about? Who are you? Who will you be tomorrow?
I'm with Sullivan on this - perhaps part of Obama's poor performance really was the completely different character he came up against face to face. Maybe he was as shocked as the nation and the pundit classes were. I mean, Romney has run on an extreme Right wing platform so far, then showed up to the debate as a mild centrist who cares more about medicare and poor people than the millionaires he's actually running for.
Anyway, Obama really needs to find a way of using this against Romney and paint him as a sociopathic liar (which he clearly is), or he risks allowing Romney back into the race. Romney won't stop lying, but Obama can start pointing it out.