Clinton's Reasoning

Fallows theorizes why the Clinton campaign attacked Obama so shamelessly:

The Clinton team doesn't worry about hurting Obama's prospects of winning in the fall, because they assess those prospects at zero. Always have. Obama might not win if he leads a bitterly divided party, but (in this view) he was never going to win. Not a chance. He would be smashed like an armadillo in the road by the Republican campaign machine, and he would be just about as ready as the armadillo for what was coming.

The distinguishing characteristic of the Clintons has always been a reverence for the Republican attack machine, and the concomitant low opinion of the American public it requires.