After mapping Florida's electoral history and looking at the outlook there for this cycle last week, I was curious what the equivalent charts for Pennsylvania would show. Pennsylvania was one of the three Rust Belt states that flipped in 2016, eroding the Blue Wall in the North that previously seemed unlikely gains for Republicans. Trump very narrowly carried Pennsylvania, Michigan, and Wisconsin, with less than 45,000 votes in each state differentiating the candidates and ultimately determining which way the electoral college swung.
This time around, Biden holds a more comfortable lead in polls in Michigan and Wisconsin than Clinton did, yet Pennsylvania and its relatively larger electoral vote count appear en route to another outcome defined by the slimmest of margins. Jackson Bryman notes on Twitter that the discrepancy in polling can likely be attributed to "1) rural Michigan and Wisconsin are not Appalachian; those areas (WI/MI) are much less culturally conservative." and "2) 'Rural' Appalachian Central PA is actually quite populous."
Trump flipped only three Pennsylvania counties in 2016, driving many parts of the state more deeply red than they already were. Biden looks to shore up the Dem 2018 midterm gains in the Philadelphia suburbs (Chester, Montgomery, and Bucks counties) while taking back counties like Erie from Trump, the bellwether that was one of the three to switch from blue to red in 2016.1
In the homestretch of the cycle, the RealClearPolitics poll average has shown a considerable amount of tightening, with Trump closing much of the polling gap that has existed for months. The 538 polling average, however, has Trump gaining less ground, and the 538 win probabilities for either candidate have held steady since mid-October. Betting markets seem to be more closely tracking the RCP average and likely have involve seekers looking for another upset a la 2016.