Hillary Clinton won a decisive ten-round decision over Barack Obama in Pennsylvania's Democratic primary, but she didn't score a knockout. The struggle continues. Clinton still has virtually no chance of overtaking Obama's delegate lead or his edge in the popular vote. And the superdelegates will be loath to ignore this advantage. Meanwhile, Obama's weaknesses as a general election candidate grow more apparent with each successive primary.Clinton's best chance of winning the nomination was to win Pennsylvania so decisively that she would have set off a media firestorm about Obama's electability--one that would lead superdelegates to wonder whether she would not...