Hmm. Really, the message the Obama camp needs to play up next is "What are they afraid of?". McCain's left himself terrbly vulnerable, IMO: between refusing to let Palin do more than a tiny number of interviews and then finding a convenient excuse to postpone the debate, he's susceptible to a (quite possibly true) charge of political cowardice. It's uncomfortably Bushian: this sort of rigorous avoidance of anything that might not go perfectly according to message is a technique honed by the current Administration.
It's not Obama's style to say anything quite so overt in person: he prefers to stay polite. But I'll be surprised if they don't find a way to inject that meme into the political discussion. McCain's whole image is built around soldierly courage; this means that his weak spot is charges that he's mostly full of bluster. There's some real truth to that (ranging from his foreign policy to his campaign style, he has shown a love of showy risk but fairly poor calm resolve), and his current move is especially susceptible to it.
The other message, that needs to be hammered home today, is "A good President needs to be able to do multiple things at once". While it's admirable and correct to focus mostly on the business at hand, he really *should* be able to deal with one debate while that's going on. The world is not so simple as to allow you to put all but one crisis on the back burner. (Indeed, the tendency to ignore inconvenient messes is one of the Bush Administration's worse traits: they generally let many problems fester while they focus on one at a time...)