Brendan Nyhan pronounces himself confused:

I don't understand her endgame. One interpretation is that she's trying to solidify her position as the frontrunner for 2012 if Obama loses in November, but she's generating so much resentment among Obama supporters that it will arguably damage her standing within the party.

I've heard a lot of political junkies reason along these lines over the past month or so, but it's borne out by the data. Clinton's favorability rating among Democrats has taken a hit, but it's been a small one, and she's still very well-liked by most Democrats (as is Obama). Whatever her subjective intentions, her past month of campaigning has succeeded in harming Obama's chances in 2008 without measurably damaging the prospects for an "I Told You So" primary campaign in 2012. For a long time, I've kept believing that Clinton's desire to run again in 2012 if Obama loses in November would get her to drop out of the race in order to avoid unduly alienating people, but as we can see her decision to drag this thing out doesn't seem to have actually alienated many people thus far.