Just to add a bit to Mike's thoughts on the Register poll--Obama's lead is clearly driven by three factors: His lead among first-time caucus-goers, his lead among independents, and his lead among young people. What's interesting about the poll is that all of these groups make up a larger portion of its likely caucus-goers than in most previous polls. So the Register is basically saying that the groups that disproportionately favor Obama are much more likely to turn out than they have in the past. Now, the Register has a reputation for being the gold standard of caucus polling, so that may well be true. Or the paper could be way off the mark. But the thing is, it may not matter either way. That's because the Register poll isn't just a description of what's going on. More than any other poll, it actually influences what goes on. Iowans will wake up tomorrow to find a headline that says, "Obama Widens Lead Over Clinton." And, human psychology being what it is, that may well push them into the Obama camp Thursday night.

--Noam Scheiber