A head to head comparison of the 2016 Primary gives us an idea of the break down of the voters.
Hillary Clinton got 29% of the vote to beat Donald Trump by 1% (892K votes) and Bernie Sanders by 6% (719K votes) when the 3 are competing for the votes.
Donald Trump wins 58 out of the 67 counties in the state of Pennsylvania to support his claims of his movement in the country. This is a massive majority of the counties, a little over 7 times as many as Hillary Clinton. Bernie Sanders on a head to head match only won a single count in the state.
Bernie Sanders vs Clinton
Hillary Clinton vs Donald Trump
Donald Trump vs Bernie Sanders
The top 3 vote comparison has this to tell: Hillary Clinton (56%) beat Bernie Sanders's (44%). There was a tight race between Hillary Clinton and Donald Trump. Clinton went ahead with a 1% win. The General Election was a close race among them. Bernie Sanders lost to both Hillary Clinton and Donald Trump by over 198K votes and over 172K votes respectfully.
These 10 counties play an important role in these primary elections. Unlike in California, in Pennsylvania, top county is not an order of magnitude larger than the other counties. Even though a candidate, can get a sizable majority in a large county it is possible for the other candidate to catch up from the smaller counties.
Philadelphia does not even show up in Donald Trump's top 10 vote counties, which means he got less than 10% of the vote there. However, he was able to make up difference through the wins in his 58 counties. It also could mean in Pennsylvania, that the Democrat voters seem sensitive to the differences in Clinton and Sanders platform.
Related References: 2016 Pennsylvania General Election Story, 2020 Pennsylvania Primary Election Story