President Joe Biden will mark the anniversary Thursday of the January 6 storming of Congress by Donald Trump's supporters with a plea to save the United States from becoming a country where political violence is the "norm."

Speaking from Statuary Hall in the Capitol -- the scene of violent assaults by a Trump mob trying to stop certification of Biden's 2020 election win a year ago -- the president will warn of a dark future unless Americans defend democratic elections.

"Are we going to be a nation that accepts political violence as a norm?" Biden will ask, according to excerpts given to reporters.

"Are we going to be a nation where we allow partisan election officials to overturn the legally expressed will of the people?" the veteran Democrat will continue.

"We cannot allow ourselves to be that kind of nation," he will say, urging Americans to "recognize the truth" and not live "in the shadow of lies." 

White House Press Secretary Jen Psaki said Biden will call out Trump's "lies" in propagating the conspiracy theory that he was the real winner of the election and will recall his "horror" at the events on that "dark day."

The event, where Vice President Kamala Harris will also speak, is scheduled for 9:00 am (1400 GMT), followed in the afternoon by a prayer vigil.

Such are the depths of division 12 months later that many senior Republicans won't even show up.

The party's top lawmaker, Senator Mitch McConnell, is leading a delegation to a funeral of a recently deceased senator some 600 miles (965 kilometers) away in Atlanta, Georgia.

And Trump, after initially planning to try and steal the limelight with an anniversary press conference in Florida, issued a statement dismissing the ceremonies as Democrats "congregating... to fan the flames of a divide that THEY created."

Biden to hit at Trump 

Biden, 79, took office promising to bring old school decency and calm back to Washington. That has had little effect, however, and on Thursday, he will respond with his own offensive.

Until now, Biden has mostly opted to ignore Trump, even as the Republican continues his unprecedented campaign to discredit the 2020 election and claim, fraudulently, that he won.

Apparently, no more.

"I would expect President Biden to lay out the significance of what happened at the Capitol and the singular responsibility President Trump has for the chaos and carnage," Psaki said.

"He will forcibly push back on the lies spread by the former president in an attempt to mislead the American people and his own supporters."

Asked if Biden would use Trump's name, Psaki said: "I think people will know whom he's referring to."

- US democracy facing 'abyss' -

On Wednesday, the Capitol police chief, Thomas Manger, said his forces would never be caught unprepared again, as they were last year.

But the political risk may be, if anything, higher than before.

Writing in The New York Times, former Democratic president Jimmy Carter said Wednesday that the United States "teeters on the brink of a widening abyss."

"Without immediate action, we are at genuine risk of civil conflict and losing our precious democracy. Americans must set aside differences and work together before it is too late," Carter wrote.

Democratic Senate Majority Leader Chuck Schumer also called for a profound look at the state of the nation.

"Without addressing the root causes of the violence on January 6, the insurrection will not be an aberration -- it could well become the norm," he warned.

Attorney General Merrick Garland said Wednesday that authorities have so far arrested and charged about 725 people in connection with the attack.

Facing criticism that the Justice Department has moved too slowly in addressing accusations of a deeper plot to overthrow the election, Garland suggested that investigators are moving up the chain.

The department is "committed to holding all January 6th perpetrators, at any level, accountable under law -- whether they were present that day or were otherwise criminally responsible."