As expected, Hillary Clinton won the Pennsylvania primary. In her victory speech, Clinton said:

It's a long road to 1600 Pennsylvania Avenue and it runs right through the heart of Pennsylvania.

Demographics foretold Clinton's destiny. Barack Obama won Philadelphia, Harrisburg and a few majority-black rural counties, but Clinton took the rest of the state. Exit polls show the racial divide. Obama received 92 percent of the black vote to Clinton's eight percent. Clinton won 62 percent of the white vote to Obama's 38 percent. Clinton won white voters of all ages, including 51 percent of independents and voters age 18-29.

Clinton's victory keeps her in the game and bolsters her case that she is more electable in the general election. While Obama maintains a slim lead in pledged delegates, the Democratic nomination race is increasingly about race.

Twenty percent of Pennsylvania Democrats said the race of a candidate mattered. More revealing, 17 percent say they would vote for McCain or stay home if Clinton is the nominee. Twenty-five percent would vote for McCain or not vote if Obama is the Democratic standard-bearer.

Obama won Philadelphia with 65 percent of the vote. But he needed to win in a landslide to offset his limited appeal among blue-collar workers and voters who "cling to guns or religion." Obama's Philly margin might have been bigger if he had not bypassed campaigning in predominantly black areas, including Rep. Chaka Fattah's congressional district.

Exit polls suggested the race would be close but Clinton won by 10 points. Polling history tells us that in matters of race, voters lie. So it was wishful thinking to believe that the Jeremiah Wright, "typical white person" and Bittergate controversies would not weigh on white voters' minds in the privacy of the voting booth.

In this history-making primary season, race has become the Democratic Party's Achilles heel.