After hundreds of millions of dollars, countless rallies, events, forums and debates, controversies and scandals, the winner of the 2016 election is likely to come down to Pennsylvania.

Up to a dozen other states are important and have large roles to play in the presidential drama, no doubt. Barring some extraordinary event, the Keystone State will live up to its nickname as both parties build their bridges over Pennsylvania to the White House.

Recent public polling in Pennsylvania shows a toss-up race between Hillary Clinton and Donal Trump. Clinton maintains a 4-point edge in the RealClearPolitics average of polls, largely because of a late-April NBC survey that showed her leading Trump by 15 points. That NBC survey is wildly divergent from other polling and is likely an outlier.

Beyond its bounty of 20 electoral votes, Pennsylvania is critical this election for another reason. Trump’s unconventional candidacy is premised on this ability to attract more blue-collar and white working-class voters to the Republican party. Trump has made opposition to globalization and poorly negotiated trade deals a central argument in his campaign. The economic deterioration of states like Pennsylvania is itself a predicate to Trump’s principal campaign message.

If Trump is able to put Pennsylvania’s electoral votes in play, his message may well resonate in other rust-belt states in the upper Midwest. Not only would Ohio be safe for Republicans in November, but the party may be especially competitive in Michigan and Wisconsin this year. A competitive battleground in these states would force the Democrats to expand considerable resources shoring up states they have previously taken for granted.

If, however, Trump fails to make Pennsylvania competitive this Fall, it would be a clear indication that his message is unable to reshuffle the electoral map in the way he needs to win. If the electoral battleground this Fall is the same as in 2012 or 2008, Republicans will be at a distinct disadvantage, due to demographic changes in the old swing states.

In primary elections, Trump dominated the Republican field in Pennsylvania, capturing 57 percent of the vote in a three-way contest. Texas Sen. Ted Cruz finished second, but 35 points behind Trump. In the Democrat primary, Clinton bested Vermont Sen. Bernie Sanders by 12 points, 56-44. This strength was visible in the large crowds who attended his rallies, including an April rally in Wilkes-Barre, shown above.

Tellingly, almost as many votes were cast in the Republican primary as Democrat this year. In 2008, over 2.2 million votes were cast in the Democrat primary and just around 800,000 in the GOP primary. In 2008, there were 4.2 million registered Democrats in the commonwealth. Today, there are 4 million registered Democrats. The number of registered Republicans in Pennsylvania, 3.1 million, has been steady from 2008.

The 200,000 drop in Democrat registrations since 2008 almost equals Obama’s 300,000 vote margin over Mitt Romney in 2012.

In the lead-up to the primary election this year in Pennsylvania, 63,000 Democrats and Independents switched their voting registration to the Republican party. Just over 40,000 Republicans and Independents switched to the Democrat party.

By contrast, in 2008, more than 40,000 voters switched to the Democrat party statewide ahead of that primary, while only 1,800 switched to the Republican party. In 2008, Barack Obama won Pennsylvania by 10 points. In 2012, he beat Romney by 5 points in the Keystone State. Al Gore bested Bush by 4 points in 2000, while Kerry edged Bush by just 2.5 points in 2004.

A recent poll of a bellweather county in Pennsylvania shows Trump well positioned to compete, and possibly capture, Pennsylvania’s 20 electoral votes. Luzerne County in east Central PA has almost perfectly matched the statewide vote in every election since 2000. In the last 4 Presidential elections, Democrats victory margin in the county has matched their winning margin statewide. Home to economically depressed Scranton-Wilkes-Barre, it ought to be most open to Trump’s nationalist, economic message.

According to a recent poll of the county by Axiom Strategies, it is. Trump currently leads Clinton in the county by 17 points, 51-34. Trump has a +11 positive favorable rating in the county, while Clinton’s favorable rating is -21. Perhaps more importantly, Trump pulls support from 34 percent of Democrat voters in the county. A bare majority of 50 percent of Democrats support Clinton.

The vote in Luzerne doesn’t decide how the state will vote. For almost 20 years, though, it has been an almost perfect predictor of how Pennsylvania votes.

Every election, the Presidency comes down to a handful of states that individually represent some aspect of the American body politic. Whether changing demographics in the West, internal migration reshaping the South or the economic pain changing the politics of rusting industrial states, winning the White House requires capturing subtle shifts in political leanings in a country that is almost evenly split nationally.

The November contest between Donald Trump and Hillary Clinton is likely to be one of the closest elections since the 2000 contest between George W. Bush and Al Gore. In that election, Al Gore was trying to succeed Bill Clinton, whose approval rating was 58-60 percent ahead of the election, and benefited from a relatively healthy economy. (The economy didn’t dip into a recession until after the election.)

In 2000, in fact, the top issue for voters was Education, followed by the economy and health care. Creating better paying jobs was 8th on the list of voter concerns. In retrospect, its stunning that Bush won the election, given the mix of issues that dominated the campaign.

President Obama’s approval ratings, by contrast, are in the low 50s and the economy is viewed, at best, as stagnant and, at worst, very near a recession. The economy and creating jobs are the top two issues for voters, by a significant margin. National security and terrorism is the 3rd top issue for voters.

Whereas both Bush and Gore had very positive personal poll numbers in June 2000, both Clinton and Trump have historically high negatives. Over 60 percent of Americans have a negative view of Trump, while 55 percent have a negative view of Clinton. Almost 30 percent of Democrats have a negative view of Clinton, while one-third of Republicans have an unfavorable view of Trump.

In almost every important way, in other words, the 2016 election is completely unlike the campaign in 2000. It shouldn’t be surprising, then, that the make-up of the electoral battleground would be different as well. The story of Presidential elections throughout the 2000s has been one of Democrats making traditional Republican states competitive.

Trump, at this stage, possibly has a path forward to break that narrative and even reverse it. In many parts of the country, economic anxieties have turned into nearly existential fears. If Pennsylvania turns red, its clear indication that Trump’s core message can reshuffle the electoral deck. If Trump falls flat in the Keystone State, however, its a sign that changing demographics in the West and South control the future of American politics.