From what I can tell by cursory search, Bucks and Chester were very close between Romney and Obama in 2012.
Romney won Chester by about 1000 votes. Obama won Bucks by less than 4000 votes. Montgomery and Delaware counties are where Obama was strongest outside of Philly. Now, Luzerne County further north went for Obama by about 6000 votes and that’s the bellwether county for the state, and I believe Trump is polling way ahead there for what it is worth.