The last time Pennsylvania voted to elect the Republican presidential nominee was in 1988, but you wouldn't know it from the way people talk about the Keystone state. Although Pennsylvania has been described as a must-win in many election cycles, that isn't strictly true. Just ask George W. Bush, who served two terms without ever winning Pennsylvania. Its 20 electoral votes make Pennsylvania an enviable prize for any candidate, though. While Donald Trump's campaign has said they have a plan to the White House without Pennsylvania, he will have a tough time winning the election without it.
As FiveThirtyEight notes, while Philadelphia and its surrounding area have become increasingly Democratic each year, the rural area — often referred to as Pennsyltucky — gets more Republican. Polling aggregators have shown Hillary Clinton with a slim but consistent Pennsylvania lead, though Trump did look poised for a comeback when his numbers improved at the end of July.
A recent New York Times poll cites Trump's significant support amongst white, working-class voters, particularly ones who do not have a college degree, as his best chance of winning the state. Trump will rely heavily on that demographic in Pennsylvania and throughout the Rust Belt, including with other major potential swing states like Ohio.
If Trump does win in Pennsylvania, then, it bodes well for a Buckeye victory, too, since it would likely indicate that he successfully mobilized that group, particularly in the face of Clinton's more diverse voting coalition. For example, in July, it was widely reported that Trump earned zero percent of the Pennsylvania black vote. To be fair, his standing has improved since then—he is now polling at about one percent with African-American voters in Pennsylvania, according to a polly by the New York Times and Siena College Research Institute.
Mobilizing his white base, therefore, seems key to a Trump victory. The only other likely way Trump could win Pennsylvania is by successfully wooing the suburban white woman who make up another of the state's key demographics.
This demographic, recently parodied by Tina Fey and Jimmy Fallon on Saturday Night Live, could cast the critical votes that either keep Pennsylvania safe for the Democrats or turn it red for the first time in decades. Both campaigns seem acutely aware of this. Clinton surrogates Elizabeth Warren and Bill Clinton have been actively rallying supporters. After Trump's standing with Pennsylvanian women was jeopardized by the release of a hot-mic tape in which he described groping women without consent, Trump surrogate and daughter Ivanka was dispatched to the state in an attempt to repair relations.
Clinton's chances are looking good in Pennsylvania. But if there's one thing that's certain about this election, it's unpredictability, and it won't really be over until election night.