Noam Scheiber suggests that "the thinking in the Obama camp seems to rest on two assumptions. The first is that the press will do the work of deciphering his overly-subtle jabs at Clinton. The second is that Edwards, in moving aggressively to take on Clinton, will drive up his own negatives in addition to hers."
This sounds a bit weird, but it's basically what the Kerry campaign did in 2004. I'm pretty sure the strategy was explained in Shrum's book (though I don't have the cite in front of me), but the Kerry camaign basically held its fire all through the fall, letting Gephardt and Dena maul each other in Iowa. Supporters and strategists attacked them for their apparent lethargy even in the face of a seeming electoral deficit. But Shrum's thinking was that they were everyone's second choice, would lose that distinction if they went strongly negative, and so the only way they could win was to bide their time and let the other's destroy each other. When asked, internally, what would happen if Gephardt and Dean didn't cooperate Shrum's reported answer was that the Kerry campaign would lose. That seems to be the thinking of the Obama campaign, too.
