Although John McCain has wrapped up the Republican presidential nomination, his name will be joined on the GOP ballot by Mike Huckabee and Ron Paul.
In addition, the primary in Philadelphia features a Democratic contest in the state Senate district long served by Democrat Vincent J. Fumo, who is facing fraud and obstruction-of-justice charges and has decided not to seek another term.
Other key races include a Democratic fight for the nomination to be state treasurer; a Republican battle in the suburban Senate district being vacated by Democrat Connie Williams; and two city charter-change questions.
The Clinton-Obama primary, which begins the final phase of the prolonged nomination fight, will be judged not just on the basis of who wins but also by how much. And that, in turn, could depend on what late-deciding voters end up doing.
Yesterday, the Clinton campaign launched one last commercial aimed at late deciders who, in other hotly contested states, have put a premium on her experience and have broken her way.
An Obama victory by any margin in Pennsylvania would be a devastating, perhaps fatal, blow to Clinton's prospects. Even now, many analysts say it is virtually impossible for her to take the lead in delegates or popular vote by the close of the primary season, June 3, regardless of what happens today.
And a narrow Obama loss would do little to change the overall dynamic of the race, although the Clinton camp would try to make as much of the result as possible.
On the other hand, a substantial Clinton victory would prolong the nomination process through the next set of primaries, in Indiana and North Carolina next up on May 6, and perhaps beyond.
It would bolster Clinton's case that voters harbor lingering doubts about Obama, that she has the better chance against McCain, and that the party's undeclared superdelegates should stay undeclared to see how the saga plays out.
The two campaigns were busily playing the expectations game yesterday.
