America's moment of truth as Trump makes his last stand and Republicans face losing the Senate

Video report by ITV News Washington Correspondent Robert Moore

America will today face its biggest constitutional challenge for a generation.

It will be the President's last stand, a display of defiance and belligerence that is testing America's political system to near breaking point.

Donald Trump is embracing wild conspiracy theories about election fraud and demanding that November's already-certified election results are overturned.

Vice president Mike Pence will have the unenviable task of overseeing today's joint session of Congress as it votes to confirm Joe Biden's victory.

People attend a rally at Freedom Plaza Tuesday in Washington in support of President Donald Trump. Credit: AP

Normally, this Congressional procedure is a mere technicality. But with a dozen Republican Senators, and a hundred Republican members of the House of Representatives, threatening to challenge the result, there is the potential for political turmoil.

It is exquisitely painful for Pence who finds himself caught between the hallowed US constitution and the fury of his boss.

And the battle in Congress may not even be the greatest drama of the day.

Donald Trump has urged his loyalists to turn out and flood the streets of Washington. Multiple rallies are planned. Undoubtedly, that will bring a mix of nationalists, far-right groups, and militiamen into the capital as Congress takes its fateful step to validate Biden's victory.

Around 11am - 4pm UK time - Trump will address the crowd. That will be a big moment. Will he galvanize the partisan crowd to a still greater outrage? Might it spill over into violence?

And wait for it. There is another whole parallel political story unfolding this morning.

In the southern state of Georgia, with counting almost complete, two Senate races will be decided today, and it looks like the Democrats will win both.

That means the Democrats will seize control of the US Senate, a major boost for Joe Biden as he seeks to enact his ambitious agenda.

Once more, Trump is playing with fire by accusing Democrats in Georgia of election fraud.

Today sees a unique convergence of events in American politics: Mass rallies by angry Trump loyalists, Congress voting to validate the controversial presidential election, and the result of senate races that will determine who has control of the upper chamber.

And in the background, like a wounded animal, is the outgoing President of the United States, vowing to fight on until the bitter end.