I really enjoyed looking at this map showing the shift in each district of PA-18 from the 2016 election. Even in the hinterlands of Pennsyltucky (and maybe especially in the hinterlands), which is what we consider to be “Trump country”, there was what appears to be a massive shift.

I think the Cook Report had this district as R+11 (meaning, Republican by eleven percentage points, I think). Paul Ryan’s district is rated as R+4.

From https://www.nytimes.com/interactive/2018/03/13/us/elections/results-pennsylvania-house-special-election.html