This may be wishful thinking, but it’s just possible that the Clinton campaign has overplayed its hand on the “bitter” non-issue. When it comes to most politicians, if you can get them angry they’ll say dumb things and just dig the hole deeper. But Barack Obama knows how to use his anger. It’s not a pretty sight, if you’re the target.
Notice that he’s still pulling his punches just a little bit, in the interests of party unity for November: he mentions Mark Penn as a shill for the Colombian government, but not Bill Clinton.