Obama can win the Democratic nomination even if he loses the Pennsylvania primary. But PA may be an excellent proving ground for testing his November prospects with one of the largest groups of swing voters, the white working class. As Kate Sheppard explains in her post in today’s American Prospect:

The question for months has been whether Barack Obama can appeal to the working-class, white demographic that has been Hillary Clinton’s stronghold. It propelled her to victory in Ohio, and has appeared to remain solidly behind her throughout the primary. But with nearly three weeks still to go before Pennsylvanians head to the polls, Obama is taking his campaign directly to these voters — and fine-tuning his populism in the process. It’s a good exercise for a candidate who will need the support of blue-collar, swing voters in the general election.

Obama has tweaked the “soaring rhetoric” of his earlier speeches to more effectively connect with the bread and butter concerns of PA workers, according to Sheppard and Michael Powell in his New York Times article “Obama Is Moving to Down-to-Earth Oratory.” As Powell notes:

Mr. Obama’s effort to master a plain-spoken and blunt language that extends back centuries in Pennsylvania is accompanied by no small stakes. Voters here, as in neighboring Ohio, where Mr. Obama lost the white and aging blue-collar vote, tend to elect politicians whose language rarely soars and whose policy prescriptions come studded with detail.

It may be working. Some recent polls indicate a narrowing of Clinton’s lead, as TDS noted yesterday.
However, PA is not the perfect test for winning white working class voters because the demographic is skewed toward older workers, as Powell explains:

Mr. Obama grabbed a big chunk of the male working-class vote in Wisconsin, and another chunk in Virginia and in Maryland. But Pennsylvania is both blue-collar and aging — it has the third highest median age in the nation. And that has proved to be a troublesome demographic for him and a rich target for Mrs. Clinton.

If Obama wins PA, or does substantially better than expected, McCain will have a lot to worry about with this pivotal constituency.