The problem for pollsters is that, at this point, no one is sure how to weight Democrat vs. Republican participation. How much of a partisan edge do Democrats have over Republicans? Not clear. But how that's calculated has a lot to do with what kind of results pollsters are getting. Put wrong information in, get wrong information out.
Same goes for the extent to which "leaners" are pushed to choose a candidate. If those who are truly undecided are forced to choose a candidate for purposes of the poll, it offers a mistaken impression of how many voters are still "convinceable" for the candidate who's behind.
So nobody really knows what's going to happen on election day.
That's why it's important for Republicans to keep pushing, and for John McCain to keep hammering home the message that an Obama presidency means two things:
1. Deep economic trouble at home (as the wealth is "spread" through tax increases that will increase the pain of the coming recession); and
2. Foreign policy crises abroad, as Joe Biden has noted -- and where Barack Obama has signalled that he will answer aggression with . . . good emergency response, and lots of talk.