This really is quite the weird (and for the gullible) campaign narrative. It's true that if a Republican wins Pennsylvania there's a good chance they're going to win the election, but that isn't because they've won Pennsylvania, it's because if they've won Pennsylvania they've probably won in a bunch of other states and completely destroyed their opponent.
So, yes, the GOP can win Pennsylvania in the sense that they can win a landslide election. It's possible. But it's about the landslide, not about PA.