Joe Biden on Thursday forcefully denounced Donald Trump for spreading a “web of lies” about the legitimacy of the 2020 election in a desperate attempt to cling to power, accusing the former president and his allies of holding a “dagger at the throat of American democracy”.

The US president condemned his predecessor’s efforts to overturn the 2020 election as a “failed” pursuit, but one that continues to imperil American democracy one year after the 6 January insurrection at the US Capitol, when a violent mob of Trump loyalists breached the Capitol in an effort to stop the certification of Biden’s presidential election victory.

In a speech from the Capitol marking the first anniversary of the deadly assault, Biden was unsparing in his assessment of the harm caused by the “defeated former president” whose “bruised ego matters more to him than our democracy or constitution”.

“For the first time in our history, the president had not just lost an election, he tried to prevent the peaceful transfer of power as a violent mob reached the Capitol,” Biden said, never mentioning Trump by name. “But they failed.”

And yet the falsehoods and conspiracies that were a precursor to the violence still persist, Biden warned. He asked Americans to recommit to the protection of the nation’s 200-year-old system of government.

“At this moment we must decide: what kind of nation we are going to be?” Biden said, speaking from the National Statuary Hall in the Capitol’s inner sanctum, one of several spots overrun and defiled by rioters on 6 January. He warned: “The lies that drove the anger and madness we saw in this place, they have not abated.”

Trump originally planned to hold a news conference from his Mar-a-Lago resort in Florida on Thursday evening, but canceled amid pressure from Republicans and conservative allies who worried it would be a harmful distraction.

But that did not prevent Trump from issuing a series of furious statements in which he continued to perpetuate the “big lie”, claims that were rejected by dozens of courts, Republican election officials and members of his own administration.

“They got away with something, and it is leading to our country’s destruction,” Trump wrote in one such salvo that made no mention of the violence that occurred in his name that day.

Four people died in the chaos of the hours-long siege, as rioters overran police barricades, wielding flagpoles and fire extinguishers to break windows and battle law enforcement officers. One US Capitol police officer, Brian Sicknick, died a day after being attacked by rioters and 140 police officers were injured.

Most Republicans were physically absent from the Capitol on Thursday, with many of party’s senators, including the Senate minority leader, Mitch McConnell, traveling to Georgia for the funeral of their former colleague Johnny Isakson, who died in December.

In a statement, McConnell called the attack “antithetical to the rule of law” and said he supported efforts to hold accountable those who broke the law.

But he did not denounce Trump as he and many Republicans did in the aftermath of the attack. But a year on, the shock and revulsion have dissipated, and Trump remains the most powerful and popular figure in a Republican party, and questions about the legitimacy of Biden’s election have become a litmus test for candidates seeking the former president’s endorsement.

Biden’s speech opened a day-long program of events on Capitol Hill to mark the anniversary.

Throughout the day, members grew emotional as they recounted their memories of the insurrection – the sound of pounding fists at the door of the chamber, the whirring of the escape hoods, the shock of a Confederate flag in the hallowed halls.

Others recounted quiet moments of grief and acts of heroism – the bravery of the police officers who defended the Capitol and the aides with the presence of mind to carry to safety the wooden boxes containing the electoral votes.

Presiding over the House floor on Thursday, Speaker Nancy Pelosi declared that democracy had prevailed when members returned to the Capitol after the riot to ratify Biden’s electoral victory.

“The Congress, because of the courage of all of you, rose to honor our oath and protect our democracy,” she said, before leading members – all Democrats with the exception of congresswoman Liz Cheney – in a moment of silence.

Speaking just before Biden, vice-president Kamala Harris, a former California senator who was in the Capitol on 6 January last year, said the rioters not only defiled the building but assaulted “the institutions, the values, the ideals that generations of Americans have marched, picketed and shed blood to establish and defend”.

In their comments, Harris and Biden called for the protection of voting rights. Harris urged lawmakers to pass the voting rights bills currently stalled before Congress.

The insurrection was the last desperate attempt by Trump to overturn the results of the 2020 election, after a series of legal challenges and a pressure campaign failed.

On that day, a mob of his supporters stormed the Capitol after Trump encouraged them to “fight like hell” as Congress convened to certify the election result. But lawmakers who had initially fled for their lives during the siege returned to the chamber, shaken but resolved, to make Trump’s electoral defeat official.

In the year since the attack, elected officials, historians and democracy advocates have warned that the threat of future violence remains high. Trump and his allies have spent the past months rewriting the 6 history of January, downplaying the violence and shifting the blame.

It was the the worst attack on the Capitol since it was burned by British forces in 1814.

Much of Biden’s speech was devoted to establishing fact from fiction about the events of 6 January, as a revisionist history of the attack, promoted by Trump and his allies, takes root.

“That’s what great nations do: they don’t bury the truth, they face up to it,” he said. “We must be absolutely clear about what is the truth and what is a lie.”

“This wasn’t a group of tourists. This was an armed insurrection. They weren’t looking to uphold the will of the people, they were looking to deny the will of the people,” Biden said.

All the while, Biden charged, Trump watched the violence unfold on TV from the private dining room near the Oval office. “He can’t accept that he lost.”