All told, we see a statistically significant relationship between Obama’s margin and the Democratic advantage in partisan identification. In other words, there appears to be a bimodal distribution of the polls. They are not converging around a single point. Instead, some (notably Rasmussen, Purple Strategies, Survey USA, and Mason-Dixon) see Obama ahead by just 1 to 3 points in the key swing states, while others (notably the Washington Post, Fox News, PPP, and NBC News/Marist) see an Obama lead that ranges between 4 and 8 points. And the difference looks to be built around how many Democrats are included in the polling samples.

If it comes down to whether or not this will be a repeat of 2008 — which is basically what the latter camp of pollsters is suggesting — then my money is on no. Of course, it is possible that I am wrong. I have no crystal ball looking forward. All I can do is look back through history, where I see on average a nationwide Democratic identification edge of about 3 points, which is also roughly the midpoint between 2004 and 2008. That is my guess about 2012. It is an informed guess, but it is still a guess. If I’m right, then Rasmussen, Purple Poll, Mason-Dixon, and Survey USA are closer to the mark. But I could be wrong, in which case Fox, PPP andWashington Post are closer to the mark.

Importantly, the pollsters are guessing, too…

Final thought: As I mentioned earlier, a big “tell” here is that Obama cannot build any kind of a lead among independent voters. That suggests to me that his advantage is built entirely on Democratic enthusiasm, which right now is above its historical trends and clearly on a post-DNC bump. Nobody in the postwar era has won the presidency by carrying less than 49 percent of independents, and Obama is quite a ways below that mark, even if some polls show him at or above 50 percent nationwide and in the key swing states.