In responding to those who say "don't believe the polls:"
Some argue that the polls are systematically biased against Republicans. This might qualify as a simple argument had it been true on a consistent basis historically, but it hasn’t been: instead, there have been some years when the polls overestimated how well the Democrat would do, and about as many where the same was true for the Republican. I’m sympathetic to the notion that the polls could be biased, statistically speaking, meaning that they will all miss in the same direction. The FiveThirtyEight forecast explicitly accounts for the possibility that the polls are biased toward Mr. Obama — but it also accounts for the chance that the polls could be systematically biased against him.
Others argue that undecided voters tend to break against the incumbent, in this case Mr. Obama. But this has also not really been true in recent elections. In some states, also, Mr. Obama is at 50 percent of the vote in the polling average, or close to it, meaning that he wouldn’t need very many undecided voters to win.
A third argument is that Mr. Romney has the momentum in the polls: whether or not he would win an election today, the argument goes, he is on a favorable trajectory that will allow him to win on Tuesday.
This may be the worst of the arguments, in my view. It is contradicted by the evidence, simply put.Link. And cf.: