More from today's 538 blog:
Still, this Electoral College discussion is going to be academic unless Mr. Romney can reverse his poor run of polling. We’ll conclude with a scary thought for Republicans.
Right now, the Nov. 6 forecast projects that Mr. Obama will win the popular vote by 3.6 percentage points. As I mentioned, that does account for about a two-point decline from where Mr. Obama seems to be in the polls right now. Otherwise, however, the model assumes that the uncertainty in the forecast is symmetric: Mr. Obama is as likely to overperform it as underperform it.
If Mr. Obama misses to the downside by 3.7 percentage points, then Mr. Romney would win, at least in the popular vote. However, if Mr. Obama missed to the upside by 3.7 percentage point instead, he’d win the popular vote by 7.3 percentage points, exactly replicating his margin from 2008.
In other words, there 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.