General Discussion

https://en.wikipedia.org/wiki/2016_Pennsylvania_Democratic_presidential_primary

This time around, the primary was not competitive on either side. Low turnout is to be expected. Which is why these numbers are encouraging:

In Pennsylvania, Trump won the Republican primary with 789,139 votes and 83.4% of the vote.

Meanwhile Biden won the Democratic primary with 929,361 and 93.1% of the vote.

(The tallies above were recorded with the overall count at 96% in the Dem primary and 99% in the GOP primary, so they may change but only slightly.)

Bottom line: Operating under similar circumstances -- in a potential swing state, with both candidates having already wrapped up their party's nomination -- Trump's performance, as the challenger, was much weaker than Biden's.