The south's the key. If Biden doesn't win decisively in early reporting states like Florida and North Carolina (both of which went to Barack Obama in the landslide of 2008), his campaign will be struggling to win elsewhere. If, however, he's competitive in a state like Georgia (which last voted Democrat for Bill Clinton back in 1992), well, then the swing is on even in what should be Trump's heartland. And this is the key.

The polls are picking up a huge shift in public sentiment: the question is, will this be reflected in voter turnout? When the country switches, installing a Democrat in the White House, it traditionally does so in a big way. That's what Biden's hoping for: not a slow count to victory, but rather a surging wave of blue sweeping across the map.

So what could go wrong? Here are a couple of points to remember while you're watching the show.

The first is that although today's vote will decide the presidency, America isn't a democracy. That word isn't mentioned in the constitution. It's a republic, and the system of government designed to support smaller, often conservative states. That's why for most of this century the occupant of the White House hasn't won the most votes. This is exactly what Trump's hoping for again: the possibility that voters in a few small states will overturn a thumping majority elsewhere.

The second is the voting system is rigged. Elected officials - who, by definition, have a lot to gain by fiddling with the mechanisms - decide everything. This includes things we take for granted, like where ballot boxes are (or aren't); what identification people will need to vote; how the vote will be counted. This opens the door to fraud on a massive scale. While in the past both parties have exploited this to their advantage, today most of those officials are Trump Republicans.

Any delay provides a chance for the lawyers to get involved and, with Trump now securing a majority in the highest court in the land, that's the last thing the Democrats want.

The third issue is the broader dynamic: this is why the world is watching. The obvious concern for Australia is the potential for US retreat from the world stage - yet this is almost guaranteed no matter who wins. Despite often bellicose rhetoric, Trump's first term saw decisive US withdrawals from Afghanistan, the Middle East, and South Korea. The irony is that a Biden victory will almost certainly see more of the same. America is retreating into itself. We need to prepare for a new world order.

The past decade has witnessed the triumph of conservative policies. A Biden victory would reverse this. Trump's loss could well signal the beginning of a left-wing resurrection, worldwide.

Few of those standing in long lines waiting to vote actually want a Biden victory - but they do, desperately, want the President out. This ballot is a referendum about Trump and yet, somehow, despite being in office for the past four years, Trump's completely upended the campaign narrative. He's enthusing his supporters by presenting as the outsider, the challenger, someone who's been blocked every step along the way. This is not simply an advertising triumph: it has huge ramifications for democracies everywhere.

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Social media is transforming the way we communicate. If Trump wins it will prove choosing the right message really can triumph over reality.

One week ago, as the US established daily new world records for the number of infections, the White House released a screed insisting Trump had "ended the COVID-19 pandemic". By taking "decisive actions to engage scientists and health professionals" the President had, the White House asserted, "understood, treated, and defeated the disease". It was labelled as his top accomplishment.

Think about that for a second. More than 230,000 deaths attributed to the virus; no sign of it ending. More infections than ever before at a rate climbing faster and higher than any other country. Trump is completely re-writing his record fighting the disease. This is not just an election that will decide the presidency: it's a vote that will decide the very nature of truth itself.