Maybe he wants to exert his will on the bailout bill. There's a good chance he'll be president -- he should have real influence within his party. Maybe he has donors he has to take care of.
Or maybe his Rovian advisors calculate political theater will get more votes than the debate. They could be right, they know their base much better than I do.
Or maybe McCain is not ready to be seen in a debate setting.
I've noted a few times that McCain is at risk, by virtue of age, smoking history and head injuries (Vietnam), of a dementing disorder. His erratic behavior over the past month makes that even more probable.
Cognitive disability in the aged often arises from a combination of the Alzheimer's process and vascular disease, including frequent small strokes. If he's experienced an abrupt drop in his cognition, I'd wonder about a small stroke or "micro-infarct". Typically symptoms will improve over days to a week, but usually not back to the previous status.
I'm not the only one to wonder, of course:
Daily Kos: Has John McCain had a stroke?If McCain's health is failing the trip to Washington may also involve finding someone to stand in for him.
...listen to his speech, and look at his left eye. I'm no expert, and this is pure speculation only, but could the real reason McCain has suspended his campaign be because he has suffered a small stroke?