Can Obama win the white vote?

Ken Rudin of NPR writes in Political Junkie prior to yesterday's results:

Pennsylvania exit polls showed that white voters, especially blue-collar Dems, went overwhelmingly for Clinton. Everything from his skin color to his "bitter" comment in San Francisco to charges of elitism to his association with the Rev. Jeremiah Wright has been blamed for that. All may be true. And it may portend big trouble for Obama in November. But for the record, no Democratic presidential candidate has won a majority of white voters since Lyndon Johnson in 1964.