I think it is impossible because so many people are not saying a word. Republicans, PUMAs are remaining silent.
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The UK Telegram had a recent article on where the US polls might be wrong, based on UK experience with upset victory of PM John Majors- At that time, no one would admit to pollsters that they were of the Conservative Party—so the polls predicted a huge Labor victory- but were all off.
I remember that. I'm thinking too that because the MSM has worked so hard to make Sarah Palin out to be a moron, probably a lot of people, especially women, don't want to admit they're voting for McCain/Palin. Also men may not want to admit they're voting for a ticket with a woman on it.