Washington (AFP) - A divided nation will experience an ominous split-screen moment Thursday when President Joe Biden uses the anniversary of the January 6 attack on Congress to warn of threats to US democracy and Donald Trump goes live with his conspiracy theories.

One year after a mob of Trump supporters marched on Congress to try and prevent lawmakers from certifying Biden's victory in the presidential election, political wounds remain far from healed.

Biden and Vice President Kamala Harris will reportedly speak from inside the Capitol, the setting during the unrest of almost unbelievable scenes as Trump supporters fought past police to invade the heart of US democracy.

As a veteran politician who came out of retirement to take on what he saw as Trump's authoritarian presidency, Biden has often warned during his first year in the White House of an "existential" threat to political freedoms that until now most Americans took for granted.

His speech -- part of a series of events on what Biden's key ally, Democratic Speaker of the House Nancy Pelosi, says will be a "difficult day" -- is set to take that warning to a new level.

But while Congress is holding a prayer vigil for what Biden has called "a dark moment," Trump will be giving a press conference from his luxury property in Mar-a-Lago, Florida.

His message is likewise easy to predict. Despite losing by more than seven million votes to Biden, and despite losing multiple court challenges around the country, Trump continues to tout wild claims that the 2020 election was stolen.

And the accusations are only the most incendiary element of a broader attack against Biden on everything from immigration to Covid-19, all adding up to what looks very much like an as-yet undeclared bid to take back power in 2024.

It's a campaign that Carl Tobias, a professor at the University of Richmond School of Law, calls "unprecedented in US history."

"No former president has attempted to do so much to discredit his successor and the democratic process," Tobias said.

What can Biden do?

However ludicrous the election conspiracy theory may be -- one federal judge in Pennsylvania ruled Trump's case "strained" and "speculative" -- it is seen as truth by millions of Americans.

Polls consistently show that around 70 percent of Republicans think Biden was elected illegitimately. 

A new Washington Post-University of Maryland poll puts this number at 58 percent. However, that same poll found that 40 percent of Republicans, compared to 23 percent of Democrats, believe violence against the government is justified sometimes.

Fighting what Trump, the master brander, popularizes as "the Steal," has become a political ideology in its own right, with nearly all Republican lawmakers either squirming to avoid criticizing what happened on January 6 -- or actively defending the attack.

Lara Brown, director of the Graduate School of Political Management at George Washington University, said the combination of political grifters looking to get into Trump's good books and the masses of voters deluded into believing what they're told amounts to a considerable force.

"What is so frightful about where we are right now isn't just that these are elite attacks, but they are being fueled by a grass roots movement," she said.

"It wasn't just far-right win groups who had organized" on January 6, she said. "It was average, everyday Americans who had bought into this whole notion."

It's unclear what, if anything, Biden can do to change these dynamics.

Political scientist and Democratic pollster Rachel Bitecofer urged Biden to take on Trump more aggressively, rather than stick to pretending that the man Press Secretary Jen Psaki has referred to as "the former guy" no longer matters.

Biden "is not commemorating an event that ended. He is commemorating the event that is in process and threatens to get worse," she said.

"There's a real hesitancy to accept how virulent the right is in coming after democracy here."

Brown said, however, that Biden has little room for maneuver, because a direct attack on Trump risks looking like a "political witch hunt" -- exactly what the former president claims in his conspiracy theories.