Over at the Real Clear Politics blog, Steven Stark lays out a theory I've heard batted around a bit over the last few days, about why Hillary might have decided to unload on Obama. Stark writes:

Clinton would much rather face John Edwards in the later primaries than Obama. It's true that in a three-way race, attacks usually hurt both the attacker and attackee, benefiting a third candidate. Yet that may be perfectly acceptable to the Clinton campaign on the theory that if Edwards does well in Iowa, he still ultimately doesn't have the resources or the support to run a true national campaign on February 5th. 

The problem, as a reader points out, is that there's no way to guarantee that she finishes second rather than third under this scenario. On the other hand, the Clinton campaign may believe even third isn't a disaster as long as Obama isn't first. In that case, Hillary still denies Obama the "big mo" heading into New Hampshire, where she's pretty well situated, and where Edwards, even with a post-caucus boost, probably can't catch her. Even under this worst-case scenario, the Clintonites may be thinking, Iowa becomes more or less meaningless.

I'd make two other points. First, as far as I know, Clinton hasn't aired any negative ads in Iowa, which is what most people believe creates a backlash. Some of her recent comments and campaign e-mails about Obama may seem harsh, but they were hardly the kind of day-in/day-out television blitz that really lodges in people's minds.

Second, I'm willing to believe that attacking someone tarnishes you in the eyes of voters. But, in the absence of a retaliatory attack from your opponent, I'm not sure attacking is a net negative. That is, you may diminish yourself a bit by attacking, but, if the attack is effective, it may diminish your opponent a lot more. Generally, the problem with attacking is that you both diminish yourself and invite retaliation, which can diminish you even more. (Note, for example, that the 2004 Gephardt-Dean murder-suicide scenario involved both sides airing negative ads against one another; it wasn't just Gephardt attacking Dean or vice versa.) 

The Clintonites may be assuming Obama doesn't have the stones to retaliate, in which case they may drive him to third and hang on to first or second themselves. (As I explained in my recent Obama piece, I think that's a false assumption. I suspect Obama will respond to any attack that isn't ridiculous or self-defeating on its face. But it's not an unreasonable read of his behavior to this point.)

--Noam Scheiber