At 1.35 in the morning Eastern Time on 9 November 2016 Donald Trump was almost certain to become the next president of the United States. The Republican candidate began to look like the winner in the evening of 8 November, when he clinched first Florida and then North Carolina. But it was an hour and a half into the next day that the game was virtually over: that was when Trump won Pennsylvania, a state the GOP hadn’t added to its column since 1988.

It was the first breach of Hillary Clinton’s “firewall”, which featured large industrial northern states that were supposed to be impregnable. “I was elated, but surprised that Donald Trump was able to deal an inside straight across Pennsylvania, Ohio, Michigan and Wisconsin,” said Charlie Gerow, a long-time Republican strategist in Pennsylvania. “It was remarkable what he was able to accomplish – everybody was surprised. The polls [in Pennsylvania] showed Hillary Clinton ahead by substantial margins.”

This year Pennsylvania is once again a potentially decisive state for Trump. With 20 electoral college votes at stake, and demographics that should be favourable to the Republicans, it is seen as a key battleground. But it’s a fight Trump has to win if he is to retain control of the White House.

In the 21st century Pennsylvania has something of a tattered reputation, its fate largely tied to the rust-belt region. The heavy manufacturing and extractive industries that once made it a powerhouse are a shadow of what they were, and many of the high-paying union jobs they offered have vanished. Population growth has been sluggish for decades and some parts of the state have been losing residents since the 1950s.

Even so, Pennsylvania is still the fifth largest American state by population. It’s also huge, 283 miles across, and varies dramatically in geography and demographics from region to region. There are some areas that have continued to grow in population, such as the south-eastern corner that encompasses the Lehigh Valley and the Philadelphia region. The city itself only lost a quarter of its population in the decades following the Second World War and the population has been growing since 2006: a stark contrast to other rust-belt cities – including Pittsburgh – that lost more than half their residents over the same period.

“Pennsylvania is changing electorally along regional fault lines between the south-east and the rest of the state,” said John Kennedy, a professor of political science at West Chester University. “Look at where the population overall is gaining and declining: it’s increasing in blue counties, in general, and declining in red counties.”

Pennsylvanians are increasingly concentrating in Philadelphia and Allentown at the expense of Pittsburgh and Erie
County-based population growth, 2010-19

Philadelphia and its suburban collar counties are the economic powerhouse of the state, and they are also the heart of contemporary Democratic politics in the state. Since the 1990s, they’ve mostly voted for the party’s presidential candidates and increasingly their down-ballot races have gone that way, too.

It didn’t used to be this way. Historically, Philadelphia and its suburbs were a Republican bastion. It was the manufacturing and mining-centred areas of the state that were heavily Democratic. Much of western Pennsylvania had a thriving steel industry, fuelled by rich veins of bituminous coal. At the centre of it all was the Monongahela valley, and Pittsburgh, which maintained its dominance as the steel-producing capital of the world from the 1880s through the 1950s. In the north-eastern corner, near Joe Biden’s birthplace of Scranton, was the home of an anthracite coal industry, while in the north west Erie tapped into the Great Lakes shipping trade. Democrats and their labor union allies controlled all of it.

But as manufacturing and mining faded in prominence, and the might of the industrial unions shrivelled, Republicans gained a foothold in the suburban areas surrounding Pennsylvania’s small, shrinking and terraced house-lined cities. Voters were attracted by more conservative messaging around cultural issues, such as guns and abortion, and appeals to an American identity that seemed increasingly threatened in a globalising world. Adding these new voters to the party’s long-standing rural base bolstered the GOP. Although its candidates kept losing presidential races, the races were sometimes close, the party won many other statewide elections and favourable maps mostly kept the legislature under Republican control.

In 2016 Trump capitalised on these changing dynamics, claiming to support social insurance programmes and industrial planning policy that previous presidential candidates, such as Mitt Romney, disdained. Trump also aggressively emphasised white identity politics in a way other Republican presidential candidates had avoided. The combination won him both followers in former Democratic strongholds and even deeper support in rural parts of the state.

“Donald Trump was able to appeal to working class Democrats who hadn’t historically voted Republican,” said Gerow. “He spoke their language and had a message that appealed to them: that we were going to take on China and put more money in their paychecks. He was more popular in the union halls than in the country clubs.”

Trump beat Clinton in Pennsylvania with just over 44,000 votes, out of the more than six million cast. He swept every county in the west except Allegheny, home to Pittsburgh and its heavily populated Democratic inner-ring suburbs. In the north-east, he became the first Republican since Ronald Reagan to win Luzerne County. In many rural counties, Democratic votes fell by double-digit percentage points. He won 50 per cent of white women’s votes – despite Clinton’s historic candidacy – and a crushing majority among white voters without college degrees.

Clinton, meanwhile, did fairly well in the Philadelphia metropolitan region, where she increased Barack Obama’s totals from 2012 and racked up a 663,000-vote advantage. But her weakness in counties such as Bucks and Northampton drove down her total in the Democratic mainstay of the south-east, too. The almost 50,000 left-wing voters who broke for the Green Party helped seal her fate.

Despite winning the state in 2016, Trump underperformed in some of the most populous parts
Bubbles sized by population and coloured according to whether Trump over or underperformed in the county
2016 election result

Since 2016, however, Pennsylvanian politics has not provided Republicans with much good news. The backlash against Trump’s victory began almost immediately with a wave of sustained activism. Soon after Trump took office, polls of suburban voters, especially in the populous Philadelphia suburbs, showed a move against the president. As the 2018 midterms approached, huge amounts of money were raised for Democratic candidates in down-ballot races.

“The enthusiasm of people who want to defeat Trump, which has been maintained since the day he took office four years ago, has surprised me,” said Larry Ceisler, a Democratic political consultant in Philadelphia. “From the Women’s March [on 21 January 2017] onward that level of enthusiasm and determination has been maintained.”

In the 2018 midterms the Republicans lost the suburban counties of Delaware and Chester for the first time since the Civil War. At the state level, the incumbent Democratic governor and senator won commanding victories over Republican challengers who tried to replicate Trump’s tactics. In the regions that used to be Pennsylvania’s Democratic backbone, in the south-west and north-east, Republicans took control of county governments for the first time in decades. But the Republican vote share fell everywhere when compared with 2016, including in rural areas.

The big difference between 2018 and 2020, the president’s supporters say, is that Trump wasn’t on the ticket last time. His campaign is banking on high turnout among his base to drive Republican vote totals above those of 2018 or 2016.

“The Trump campaign felt that in Pennsylvania they left a lot of votes on the table four years ago,” said Ceisler. “People who didn’t come out and vote because they didn’t think that Trump would win. They’re really trying to target those high school-educated, blue-collar people now.”

But Trump’s polling among two groups he did win in 2016 has been slipping. Conservative-leaning elderly voters have been signalling their displeasure with the president over his cavalier handling of the Covid-19 pandemic, and he has been badly trailing Biden in Pennsylvania among over-65s in a series of Quinnipiac University polls. The second group is white women, whose support for Trump has been slipping for years, prompting him to plead at a recent rally in Johnstown, Pennsylvania, “Suburban women, will you please like me?”

There is little sign that Trump has added substantially more voters to his ranks since 2016, although Trump polls better among black and Latino men than might be expected and he’s been trying to court their votes. Polls have consistently shown Biden in the lead in Pennsylvania, and the gap has not been narrowing.

“2018 was bad across the country because swing voters in the suburbs broke overwhelmingly for Democrats and Trump voters didn’t show up at the polls,” said Mark Harris, a Republican political consultant. “There’s still the swing vote or suburb problem, that’s the biggest delta between 2016 and today. But I believe the president’s voters are going to show up in droves.”

To win Pennsylvania, Biden will have to lose less badly than Clinton in rural and former industrial counties, where he has invested a lot of spending and personal attention. He made his Scranton upbringing a core part of his message – a detail that Trump tried to dispute in their final debate – and took a train tour through western Pennsylvania, meeting with building trades and the remnants of the industrial unions. Although the Democrats have previously lost many of these counties, the party retains its strength in old factory towns and small cities (even if that advantage recedes rapidly past the municipal limits). Without the Green Party on the ballot, there will likely be fewer left-wing defectors from the Democrats, while the Libertarian Party remains as a right-wing alternative to the Republicans.

Biden will also have to win large numbers of votes in the Philadelphia area. Fired-up suburbanites will be a huge part of that potential voting bloc, but the campaign is not taking the votes of city residents for granted either. Biden placed his national headquarters in Philadelphia and has held numerous rallies there, including one headlined by Barack Obama 12 days before the election. Notably, turnout among black voters in Philadelphia has barely dipped since 2012, in contrast with other large rust-belt cities where African American participation has plummeted.

Democrats and their supporters see a strong potential for victory in the poll numbers and the surge of support for their candidates in the south-eastern suburbs.

“The shifting political climate in the state has put a number of races in play that weren’t in prior cycles,” said Josh McNeil, executive director of Conservation Voters of PA. “The increased polarisation, largely around the president, has reshaped the political landscape. If you voted against the environment a lot in, say, Bucks County, it’s a lot harder to get away with it now.”

The Conservation Voters of PA and other environmental groups are spending more than $2m on legislative races in the state, hoping that 2018’s results and anti-Trump backlash will allow for down-ballot Democratic victories. The state-level legislative maps in Pennsylvania heavily favour Republicans, even in the absence of gerrymandering. Although the Democrats are very competitive in state-level races, and win a majority of votes half the time, they routinely fail to win control of the General Assembly.

This year observers say the chance of flipping the state house, where Republicans still hold many seats in the Philadelphia suburbs, is strong. To win control of the state senate, which the GOP has controlled for almost 40 consecutive years, the Democrats would have to win five seats amid a wave of tidal proportions.

But the GOP has racked up impressive voter registration numbers in 2020. Although Pennsylvania has over 800,000 more registered Democrats than Republicans, it’s long been assumed that those numbers are inflated and that many of those voters are in formerly industrial areas that have been shifting politically for a generation.

When someone actually decides to register in an election year, it means they intend to vote in that election. In 2020 Republicans have registered more new voters than Democrats. This year that gap may partly be because conservative political groups were campaigning on the streets long before Democratic groups and their allies were willing to do so. But that doesn’t explain all the Republican registrations: since 2016, the party has added 165,000 voters, compared to the Democrats’ 30,000.

“Republicans are seeing robust levels of voter registration and engagement among rural and non-college educated white voters,” said Daniel Hopkins, a professor of political science at the University of Pennsylvania. “If the current polls are right, President Trump is going to have a hard time. But even a relatively minor polling error coupled with, say, significant election administration issues make it certainly possible that he wins.”

Hopkins believes the unusual aspects of this year, which have led to the prevalence of voting by mail, could also provide Republicans with an advantage. Trump has been preaching against the practice to his voters, who are expected to vote in-person as a result. If Democrats disproportionately vote by mail, and substantial numbers of ballots arrive too late, run afoul of Pennsylvania’s bizarre rules, or are filled out improperly, that could work in the president’s favour, too.

Trump understands how important Pennsylvania is to his campaign. That’s why he’s maintained rallies and advertising in the state, even while pulling resources out of the Midwestern states, such as Michigan, that he won in 2016. But at a 20 October rally in Erie, Pennsylvania, Trump acknowledged the difficult path to victory: “Before the plague came in, I had it made. I wasn’t coming to Erie. I have to be honest.”