The emerging conventional wisdom is that Hillary Clinton fell short in the Rust Belt states because her campaign took them for granted and failed to turn out her supporters. In the case of Pennsylvania, this thesis is demonstrably false. Not only did the campaign mobilize an army of volunteers to get out the vote; it executed its game plan successfully. Hillary Clinton lost Pennsylvania because Donald Trump brought a flood of rural and small-town working class voters into the electorate.
The standard Democratic formula for success in Pennsylvania is to run up huge margins in Philadelphia and Pittsburgh and prevail more narrowly in the suburban counties around Philadelphia, creating a margin large enough to overcome the edge Republicans enjoy just about everywhere else. The Clinton campaign did so—in fact, better than the Obama campaign did in 2012.
Although Clinton’s statewide total in Pennsylvania fell just short of Obama’s in 2012, this modest shortfall was not why she lost the state. The real story is that Donald Trump ran up the score in every Republican-leaning rural and small-town county, besting Mitt Romney’s statewide total by nearly 300 thousand votes.