How did Santorum win Pennsylvania in 2000 but not Bush?

[Southern Senator North Carolina Yankee]

Cynic is right. The Philly Burbs would still vote for a Republican down ballot and PA had long had two Republican Senators even as it leaned Democrat. Republicans held onto open seats in 1958 (a big Dem Wave) and 1976 (Carter won the state). Specter also did fine in 1992.

Santorum was indeed far more COnservative then Scott, Heinz or Specter, but he had strong appeal out west to Democrats and without having yet become controversial he was well positioned to win reelection even as the state went Democratic.

And also as Doc Cynic said, you had an underfunded Democrat that never really caught fire. Also Republicans did quite a lot to emphasize the fact that Klink was pro-life in the SE part of the state, thus removing the one issue that could give Santorum a headache in that region.