The latest crop of opinion polls has generally brought good news for Democrats. The Real Clear Politics average of all the national polls has given President Obama a slight lead, after this poll of polls had shown him trailing since Mitt Romney’s post-Denver debate comeback changed the race. Even more important, polls of likely voters in the battleground states have given the president leads in most of them. This caused New York Times blogger Nate Silver to double down on his forecast predicting an Obama win. According to Silver, Obama now has an 83.7 percent likelihood of prevailing on Tuesday.

We’ll leave aside the arguments about Silver’s odds-making, which depicts what even most liberals concede is an extremely close election as a near certain Obama win. Suffice it to say, as I wrote on Thursday, Silver’s belief that Obama had a field goal lead with 3 minutes left in the game (which he may now think is more like a 4-point lead with 2 minutes left) is based on a belief that the polls he trusts are accurate. On Saturday, however, he returned to the question that has to be haunting his readers: what if these polls aren’t accurate? While he admits the possibility, he thinks it unlikely that so many surveys could be in error. That seems logical, even persuasive. But the problem with that assumption is the same as it has been for the past month. Most of the polls showing Obama ahead either nationally or in some states reflect a common bias: their sample reflects a picture of the electorate that resembles the 2008 Democratic advantage. But this year we expect the gap in party identification to be smaller. In short, unless the Democrats match or exceed the massive “hope and change” surge of four years ago, then what Silver and the Democrats who look to his column for encouragement fear will be true: all the pro-Obama state polls are going to turn out to be quite wrong.

Silver sums up this equation quite succinctly:

I do not mean to imply that the polls are biased in Mr. Obama’s favor. But there is the chance that they could be biased in either direction. If they are biased in Mr. Obama’s favor, then Mr. Romney could still win; the race is close enough. If they are biased in Mr. Romney’s favor, then Mr. Obama will win by a wider-than-expected margin, but since Mr. Obama is the favorite anyway, this will not change who sleeps in the White House on Jan. 20.

My argument, rather, is this: we’ve about reached the point where if Mr. Romney wins, it can only be because the polls have been biased against him. Almost all of the chance that Mr. Romney has in the FiveThirtyEight forecast, about 16 percent to win the Electoral College, reflects this possibility.

Yes, of course: most of the arguments that the polls are necessarily biased against Mr. Romney reflect little more than wishful thinking. …

But the state polls may not be right. They could be biased. Based on the historical reliability of polls, we put the chance that they will be biased enough to elect Mr. Romney at 16 percent.

That 16 percent chance that Silver talks about though is far more potent than the forlorn hope he implies. Quite simply, if Democrats do not have the near 10-point lead in partisan affiliation that many polls show — which mirrors the 2008 results — then the polls that show the president leading are a misreading of a race, which is either tied or actually trending in Romney’s favor.

This is a possibility that Silver and those who look to him for comfort try not to think about, but which looms large in the final days of the race. The president may have gained some ground as coverage of Hurricane Sandy diverted the public from the election and allowed Obama (with an assist from New Jersey Governor Chris Christie) to appear in control of events. But it strains credulity to believe even that advantage can conjure up a Democratic turnout that would rival that of 2008.

That’s why the polls not only could be wrong, but are likely to be wrong. Silver may be right and our expectations of a more even partisan split may not materialize. But if that isn’t the case, then November 6, 2012 will prove to be the Waterloo not only for President Obama but also for the pollsters who are predicting victory for him.