Winning them would push Biden over the 270 Electoral College finish line to take the White House.
There are plenty of votes still to count in those states, including in Democratic-heavy urban centres. For instance, there are hundreds of thousands of mail ballots outstanding in the Philadelphia area.
Voting in the pandemic in three different ways - by mail, early in person and on election day - has also added significantly to the uncertainty. Democrats disproportionally made use of mail voting, while Republicans preferred to vote in person.
Before the election, more hopeful Democrats dreamed of the possibility of a blow-out victory with a sweep in the Sun Belt. It appears that only Arizona is within their reach and that Trump closed the deal again in Florida.
More broadly, America's great divides have shone through.
Biden regularly out-performed Hillary Clinton's vote totals to make Republican states more competitive, particularly in suburban areas. But the electorate is so polarised any surge has been impossible.
Biden cannot be faulted for his determination to reach the white working-class voters who powered Trump's campaigns. He also did his best to respond to the issues that concern younger voters. And he provided a clear character contrast with Trump.
But Trump's consistent advantage over Biden on who would be best to handle an economic recovery appears to have been a crucial factor. And perhaps some of his other arguments about progressive Democrats, law and order and fracking were effective in key areas. There's also a major question over what part unsavoury online conspiracies played in keeping supporters behind Trump.
Should Trump hold on to win it would be a comeback victory for the ages, against all the odds. He campaigned hard to juice his base turnout in the final stretch, and his party put its faith in a door-knocking operation during the pandemic.
If he does win, he will leave a demoralised Democratic opposition bereft of answers and an onlooking, uncertain world wondering what comes next.
After four years in which the country's democratic framework and old alliances were relentlessly probed and found wanting, the President looked likely to pay the ultimate political price.
He was given a 10 per cent chance of winning a second term in election forecasts. His approval ratings were close to those of previously rejected presidents George Bush snr and Jimmy Carter. And yet the candidates were close in polling in toss-up states.
In 2004, when President George W. Bush faced the voters while mired in wars in Iraq and Afghanistan, enough of the electorate decided to hold to the course during difficult times.
Potentially that may have happened again despite Trump's role in presiding over a botched pandemic response in which 232,538 Americans died, and 9.3 million became infected. The US has 4 per cent of the world's population and about 20 per cent of global coronavirus cases.
The tightness of the contest puts American democracy and its electoral system in an unflattering light.
Should Trump be returned, there would be a reassessment abroad of the country's standing.
Trump has been the loudest, inescapable, and most divisive image America has projected to the world since he was first elected.
At home, the country has witnessed a pandemic, economic meltdown, nationwide racial justice protests, armed militias on the streets, impeachment, several Trump officials being arrested and jailed, immigrant children on the border in cages, a brutalising of politics, environmental rollbacks, promotion of conspiracy theories and fakery posing as facts, and sheer exhaustion at endless chaos.
With Trump having turned away from America's traditional approach to engagement with the world, and having taken a transactional approach to international relations, and snubbed democratic allies in favour of authoritarians, four more years would sound like a sentence too many abroad.
The world will have to hope the European Union, China and other countries can push hard on climate initiatives without the US.
Biden presented himself as an experienced, familiar figure ready to bring back a more normal existence.
He appeared to offer a stability and competence Trump could not provide.
While Trump whipped up packed crowds in a pandemic with ugly rhetoric and a message of division, Biden tried to convince voters that he was worthy of trust. That he would oversee recovery work, try to improve people's lives and address glaring problems.
For now, the world waits to see if there will be a re-start for the Divided States or whether the erosion of its standing in the world is set to continue.
