That's because control of the US Senate is at stake.
In the south-eastern state of Georgia, polls are open for voters to decide on two Senate seats - after indecisive outcomes on November 3.
If Democrats can seize them both, they can draw level with the Republicans in the upper chamber, with 50 seats each.
The future Vice President, Kamala Harris, would then break the tie.
That means that Biden's agenda would have a good chance of passing into law.
Donald Trump peddles more wild conspiracy theories ahead of polls opening
But if Republicans can win just one of the two Senate seats being contested, then America faces at least two years of divided government and the likelihood of political paralysis.
Every Biden initiative, every Cabinet choice, every court nomination, every legislative move, would then become a major struggle.
That's why all eyes were on President Trump last night when he arrived in Georgia to hold a last-minute rally for the two Republican senate candidates.
It was wild stuff again - a blend of conspiracy theories about voter fraud and an absolute disregard for the reality that he lost the presidential election.
In the final days of his presidency, it appears he is convinced he won a second term.
Trump shows no sign of being prepared to give up the White House. He promised to fight until the bitter end.
For nearly 90 minutes, Trump railed against his enemies - both Democrat and Republican - and gave a rambling speech that embraced long-discredited claims of election fraud.
This week represents Trump's last stand. On Wednesday, Congress meets to vote on the certification of the election results.
Normally, that is a routine technicality.
But this time, a dozen Republican Senators and over a hundred members of the House of Representatives have suggested they will dispute the election result.
That has the potential to fuel further grievances and poison American democracy.
After all, if a party doesn't accept a loss - already certified by the individual states - then what's the point in holding elections?
Even more ominously, Trump is encouraging his loyalists to flood the streets of Washington on Wednesday.
There are fears of violent clashes, and the mayor has called on the National Guard to help ensure security around Congress.
No wonder the next 40 hours are likely to be the most significant - and potentially volatile - of the entire Trump presidency.