In the Pittsburgh neighbourhood of Garfield, a queue began building outside the polling station before dawn.
Voters who had dragged themselves out of bed to cast their ballot waited in the cold for the doors to open at 7am.
But American voters are energised and keen to make their views known.
Nearly 100 million voters have already cast their ballots before today - a record for early voting in America.
While this is perhaps to be expected amid a pandemic with a spike in the number of people voting by mail, there is a sense Americans are more engaged than ever in the increasingly polarised politics of the country.
People are pushing through the challenges of the pandemic and long lines at polling stations to exercise their democratic right, and the country is on course to surpass 150 million votes for the first time in history.
Pennsylvania has been blitzed by both candidates during this campaign, with both Donald Trump and Joe Biden visiting the state up to the wire.
The rust belt state was key to Mr Trump's victory in 2016 and is widely viewed as the knife-edge of this election.
Whichever way Pennsylvania goes, the country is likely to fall too.
While Mr Biden has a clear lead in the polls nationally, it has become an increasingly tight race in Pennsylvania in recent weeks.
Mr Trump took the state by fewer than 45,000 votes in 2016. Analysts say a mere gust of wind could blow Pennsylvania blue.
Around a third of people in Pennsylvania have voted early, fewer than in the other rust belt states, and the majority of voters are due to cast their ballots on election day.
While early voting favours the Democrats, on the day voting favours Mr Trump.
State polls will have staggered closing times due to the different time zones, but the result for Pennsylvania may not be known for days.
While the state's largest cities, Pittsburgh and Philadelphia, are aiming to count postal votes on election night, many suburbs and rural areas will count into Wednesday if not beyond.
This is expected to create some election night anxiety.
Mr Trump has repeatedly demanded that the candidate leading on election night should be named the victor.
But not all the votes will be counted by this point.
On the day, votes are counted before postal ballots and Mr Trump has sought to discredit voting by mail throughout this campaign.
Calling the result early could show an incorrect result - but the president is all too aware that would likely work in his favour.
The Supreme Court recently ruled postal votes could be counted in Pennsylvania for up to three days after election day, provided they were postmarked by 3 November.
In a tweet which was flagged with a warning on Twitter on the eve of the election, Mr Trump wrote: "The Supreme Court decision on voting in Pennsylvania is a VERY dangerous one.
"It will allow rampant and unchecked cheating and will undermine our entire systems of laws. It will also induce violence in the streets. Something must be done!"
Local election officials are braced for possible legal challenges in this closely contested state which could decide the election.
Postal votes that arrive in the window between election day and the deadline will be separated in anticipation of a legal dispute.
This is not the first time a presidential election result could be decided in the courts, after the Florida vote was settled in George Bush's favour in 2000.
Unlike that election, Mr Trump is peddling the suggestion of violence in the streets, rather than quelling the unnerving idea of unrest.
Counting has always taken place after election day.
Some of the states that favoured Mr Trump in 2016 were called in the ensuing days.
Amid the unprecedented electoral climate of a pandemic, there is a need for patience and calm. The president is showing signs of neither.