Pennsylvania is not really a Rust Belt state; the eastern part of the state, from an economic perspective, is indistinguishable from New Jersey and New York, and Pittsburgh has remade itself as a successful tech and medical research center. Some of the extreme western section of the state looks like the struggling part of Ohio, but the real partisan division within Pennsylvania is the urban/rural split. Statewide elections are typically won in the suburbs of Philadelphia.
You can make a pretty decent argument that no state means more to the Democrats than Pennsylvania in 2020. The results of the 2018 election suggest that Trump’s victory there was an anomaly; there is no reason to believe that he can recover his standing with suburban women, or that he even intends to try. The Democrats’ task here in 2020, therefore, is mostly to stay on a fairly generic message, to direct their appeal to women and reachable white working men, and to avoid extreme or provocative positions on either policy or identity.