I believe the polls, but I don't believe that Romney gained 4-5% based on the debate alone. That just doesn't happen, especially not in an election with so few undecided voters. I think it is a mistake to attribute all the movement to a single cause, as if there were no other events in the last week.
Last week's debate was Wednesday night, and there was another important event Friday morning: the jobs report. So, my hypothesis is that some of the Romney bounce is due to the jobs report.
Now you think I'm nuts. The jobs report was exceptionally good, and thus presumably favorable to the incumbent. Also, didn't I just in the last post explain that it didn't matter? Am I changing my positions like Romney?
Oh, but what I explained was that the substance of the report —the facts reported—couldn't matter for the polls. But there was another event associated with the report: Republicans started spreading conspiracy theories about it, and the media treated those conspiracy theories as if they were respectable ideas. What would be the expected effect on a "low-information" voter? A suspicion that Obama is the new Nixon, of course!
So I think that the irresponsibility of the media in giving free advertising space to the nuts has been a factor in the Romney bounce, and I would guess that it may account for up to half of it.
The poll movements are consistent with my hypothesis: first came a bounce, then it appeared to fade, but then it increased again and stabilized. This can, of course, be a coincidence, as those daily movements were well within the range of normal statistical fluctuations. But at least they provide a prima facie case for two causes, separated by a couple of days.