Sorry to disappoint but I'm not sure who this helps. There's been a long-running debate about whether his support is mostly working-class whites who might otherwise support Hillary, or anti-Hillary "change" voters sure to flock to Obama. The anticlimactic truth may well be that it's always been some of both, and neither Hillary nor Obama will see a big boost. 

This will make for a great dynamic in tomorrow night's Democratic debate, however, which is now a one-on-one affair. My first instinct is that Hillary benefits from that--she's always been strongest in debates, and (with one famous exception) quite sure of herself. Whereas sometimes Barack looks slightly unsteady. But he's clearly been gaining confidence in the past weeks, so we'll have to see.

Update: John Judis breaks down some numbers over at The Plank, but concludes it's difficult to say who benefits. And Jon Cohn tips his hat to a man who helped to shape the debate.

--Michael Crowley