Looking at the polls, it's certainly difficult to see Barack Obama losing in 12 days, but as we Democrats know, anything can happen, so it's worth exploring the various factors that could cause reality to divert from what polling is showing to be a 7 point Obama lead.

One factor that might cause Obama to underperform his polling on November 4th is The Bradley (or Wilder) effect. This has been written about a lot and most of the analysis agrees that if it did exist once upon a time, it no longer does and that it's quite unlikely to be a factor in 2008. Nate Silver has a thorough takedown of the Bradley Efect in Newsweek:

So the question is why, if a voter does not intend to vote for Obama, would he or she feel compelled to lie about it? There are perfectly legitimate reasons not to vote for Obama; a voter who wanted to vote against him because of his race would have little trouble rationalizing his vote. If a voter felt compelled to lie to a pollster, he might tell them that he was voting against Obama because of his inexperience or his liberal politics--when, in fact, he was voting against him because of his race. But the pollster would still tally the vote correctly in the McCain column. By contrast, in cases where the Bradley effect existed, including Bradley's race itself, the black candidate was as much or more experienced than the white opponent. So voters found it harder to excuse their racism and may have misstated their voting intention to pollsters as a result.

Another factor, which hadn't occured to me until last night when a friend posited it to me is what I would call the "Cool Factor." It goes like this: "Of course more people are going to tell pollsters they're going to vote for Obama, voting for Obama is much cooler than voting for McCain. Doesn't mean they're going to actually vote for him." Interesting theory and one that I hadn't considered although I think it has a corrollary on the other side, which may make it a wash: the "History Factor."

Ben Smith has a moving tale from a reader who witnessed something very interesting while early voting in Ohio.

After I voted I walked out to the street to find my mother's friends surrounding our new friend Mike -- they were laughing and having a great time. I joined them and soon learned that Mike had changed his mind in the polling booth and ended up voting for Obama. When I asked him why he changed his mind at the last minute, he explained that while he was waiting for his jacket he got into a conversation with one of the ladies who had explained how the Jewish community, and she, had worked side by side with the black community during the civil rights movements of the '60s, and that this vote was the culmination of those personal and community efforts so many years ago. That this election for her was more than just a vote ... but a chance at history.

Mike looked at me and said, "Obama's going to win, and I didn't want to tell my grandchildren some day that I had an opportunity to vote for the first black president, but I missed my chance at history and voted for the other guy."

While I call this the "History Factor" it's obviously related to the "Inevitability Factor", which actually could work for or against Obama. Will Obama voters stay home because they think "he's gonna win anyway" or will it actually compel people to switch their vote to Obama? Considering the enthusiasm level of Obama supporters, I suspect the latter is more likely.

But one interesting factor that has not been discussed very much at all is yet another argument for Obama overperforming his poll numbers, which I call the "Hard to Reach Effect."Public Policy Polling has a fascinating post about it at their blog where they find that the longer they are in the field with a poll, the better Obama does because his supporters are more difficult to reach.

We conducted half the interviews for our Florida poll this week last Thursday night. The first night McCain led by 2. The data based on callbacks over the next three days gave Obama a 4 point lead.

It was a similar story in Colorado two weeks ago. The first night Obama led by 5. The rest of the field period he led by 15.

I don't think there was movement in Obama's direction in subsequent days either of those times. It's simply a matter that you have to try more times to get his supporters on the phone.

They found this to be true during the primary as well. Once they switched to longer polling periods, Obama did better and their polling actually became much more accurate.

PPP believes this accounts for the huge discrepancies in the Ohio polling that we've seen over the past few days.

Which leads me to today's Quinnipiac Ohio poll showing Obama up by 14. That's a big difference from Rasmussen and Mason Dixon's polls earlier in the week that showed McCain winning, and I think part of the discrepancy can be traced back to the length of field time. Rasmussen's was a one night poll. Mason Dixon's was a two day poll. They couldn't have done that many, or any, callbacks to get folks on the line who weren't at home on the first shot. Quinnipiac was in the field for six days, and I'm guessing they managed to get a lot more of those elusive Obama supporters polled when they tried for the third or fourth time.

For what it's worth, PPP has a new poll out of Ohio they'll be releasing this weekend whose results will mirror Suffolk more than Quinnipiac: in other words, they have Obama's lead at around 9.

So ultimately, does the accumulation of all of these and the other factors that are going to impact turnout over the next 12 days favor Obama or McCain vis a vis their current poll numbers? I'd say Nate Silver has it about right:

With so many "X factors" like race, cell phones and turnout, there is probably an extra margin of error this year. And polls aren't terrifically accurate to begin with. But there is no reason to conclude that the polls are systematically overestimating Obama's support; the reverse is at least as likely to be true. McCain, in all likelihood, will need to win this election fair and square--which means that he has his work cut out for him.