John McCain faces an uphill battle against Barack Obama in Pennsylvania. But the Arizona Senator’s prospects could get a boost from an unlikely source: Several GOP House challengers are giving some liberal Democratic incumbents reasons to worry about their own electoral survival. Commentators argue Pennsylvania has gradually transformed from a winnable GOP target to a reliable Democratic bastion over the past two decades. Ronald Reagan won the Keystone state in 1980 and 1984, as did George H. W. Bush in 1988. But since Bill Clinton won in 1992, Democrats have prevailed in every presidential election. Still, John McCain remains competitive according to the most recent polling. As in national surveys, the presumtative Republican nominee lags by only three to five percent, in Pennsylvania. Jay Cost provides a useful historical breakdown of the state and its regional trends in this piece at Real Clear Politics As Cost notes, the state has about a 4-point Democratic tilt. That means if a Republican wins nationally by 5 points, he or she should win Pennsylvania by about 1 point. Or, losing nationally by 5 points probably means a 9-point defeat in Pennsylvania. But these overall patterns mask some intra-state variation. Eastern Philadelphia is trending very Democratic, but other regions are more hospitable to Republicans. If McCain hopes to win Pennsylvania, he’ll probably need the help of a few Republican House challengers trying to knock off liberal Democratic incumbents.Yesterday, I corresponded with National Republican Congressional Committee spokesman Ken Spain about the 11th congressional district, where Republican Lou Barletta is challenging very vulnerable incumbent Democrat Paul Kanjorski: