Nate Silver isn’t ruling out a landslide:
[T]here looks to be about a 20 percent chance that Mr. Romney will win, but also about a 20 percent chance that Mr. Obama will actually beat his 2008 margin in the popular vote. The smart money is on an outcome somewhere in the middle – as it has been all year. But if you can conceive of a Romney comeback – and you should account for that possibility – you should also allow for the chance that things could get really out of hand, and that Mr. Obama could win in a borderline landslide.