Commenter stgla reminds me that there's one other thing to chew on when you consider caucus mechanics in Iowa: the possibility of formal alliances. As Dan Balz points out in his post yesterday:

Four years ago, Dennis Kucinich and John Edwards cut a deal, agreeing shortly before caucus day that if either of them failed to reach threshold in any precinct, their supporters would go and line up with the other.

Given what we know about Joe Trippi's fondness for Obama--and the fact that Edwards and Obama probably think they have a better shot in a two-person race against one another than against Hillary--it wouldn't shock me if they tried to forge this sort of alliance. If they pulled it off--a big if, of course--they could relegate Hillary to third in Iowa, which would mean big trouble for her. I have to think the Clinton campaign is privately sweating this scenario.

--Noam Scheiber