Pennsylvania is seductive to Republican presidential candidates, but un-winnable IMO. There are a range of factors at play here, mostly having to do with the way the City of Philadelphia games the system by petitioning state judges to order polls to remain open so that they can count every dead-voter in as many precincts as possible.
And really, that’s it...Philly is a vote machine for the democrats. It’s and endless supply of votes, real or imagined.