Jon Cohn makes a good point:
Conservatives will blast [Biden's] record, just as surely as liberals will (or should) celebrate it. But one of the virtues of having Biden as the vice presidential nominee is that he won't take those kinds of attacks lightly. He'll fight back. He'll remind people, rightly, that being a liberal Democrat means raising the minimum wage, making sure everybody has affordable health care, providing strong public schools, and protecting human rights. Then, he'll ask why conservative Republicans don't want the same things. That's exactly the kind of political debate this country needs. By picking Biden as a running mate, Obama has signaled that he welcomes this argument--and intends, finally, to win it.
The Clintonian defensive crouch is over.