Obama aides stressed that the campaign will not be drawn into a fight for Pennsylvania on Clinton's terms: an expensive, all-out battle focused on her. Instead, the campaign's main target will be McCain -- a point underscored by Obama when he declared himself "ready to start a great debate about the future of the country with a man who loves his country and served it bravely."
Maybe such aides don't want that "battle focused on her" but that's the battle they must fight.
It's understandable that every Democrat wants to engage with McCain. But the nomination turns on whether Clinton continues to build the momentum she captured in the last few days. She did it by attack -- allegations of unpreparedness for crises and doubletalk on Nafta. These allegations foreshadow what McCain and his cohorts will do this fall, so meeting them now is a useful and necessary test for Obama.
Even more important, going on the offense against Clinton is not only Obama's only way to win the nomination, it also is the only way for either Democrat to win this fall.