Here, at last, was the Joe Biden that anyone on vigil for America’s teetering democracy had been waiting for.

In historic National Statuary Hall at the US Capitol, a year to the day after it was overrun by an authoritarian mob, the US president gave his clearest dissection of “the big lie” and his clearest denunciation of his predecessor, Donald Trump.

It cannot have been easy for a man who spent 36 years in the Senate, sometimes reaching across the aisle to unsavoury characters, who speaks of bipartisanship with cloying nostalgia and who ran for the White House as an apostle of national unity.

Biden could have used Thursday’s anniversary to offer olive branches, finding comfort in the traditional role as head of state as an excuse to rise above political battles of the day. His instinct may have been to be as apolitical and anodyne as a monarch.

But this was the moment that the commander-in-chief realised the clear and present danger posed to American democracy by one of its major parties and former leader gone rogue. The alarmed voices of fellow Democrats, activists, journalists and historians about the state of emergency finally seemed to have got through to him.

He understood that platitudes and prayers for a miraculous Kumbaya moment will no longer do. You cannot reason with extremists whose premise about a stolen election and the insurrection being the will of the people – wrapped up in the cult of Trump – is fundamentally irrational.

You cannot debate Fox News or fascism-curious Facebook users. Instead, the threat must be looked squarely in the eye.

“We must be absolutely clear about what is true and what is a lie,” Biden said, his voice at times trembling with anger.

“Here’s the truth: a former president of the United States of America has created and spread a web of lies about the 2020 election. He’s done so because he values power over principle.”

He never mentioned the name “Trump” but he did refer to the “former president” often. In a remark that would have stung at Mar-a-Lago, Biden said: “He’s not just a former president; he’s a defeated former president.” He also noted: “You can’t love your country only when you win.”

In a 25-minute speech that sounded like campaign-trail Biden, he recalled how the Confederate flag, symbol of the pro-slavery south in the civil war, had been brandished in the halls of the Capitol for the first time a year ago.

“We are in a battle for the soul of America,” he acknowledged. “I did not seek this fight, brought to this Capitol … But I will not shrink from it either. I will stand in this breach, I will defend this nation. I will allow no one to place a dagger at the throat of this democracy.”

It was a bracing call to action from a president accused of spending too much of his first year in office cutting deals with Republicans, for example on new roads and bridges, rather than throwing himself into the arena in a bare-knuckle fight over voting rights.

It was also clear evidence that Barack Obama’s celebrated 2004 convention speech – “There is not a liberal America and a conservative America – there is the United States of America” – no longer meets the moment. It would be as naive as claiming that America no longer sees race.

But will it make a difference? Most Republicans, including leaders Mitch McConnell and Kevin McCarthy, are not even in town. Rightwing media dismissed the speech as divisive. Trump was quick to issue a statement that said Biden “used my name today to try to further divide America. This political theater is all just a distraction from the fact Biden has completely and totally failed.”

With divisions having only calcified since 6 January, that is likely to be the Republican message going forward. But now, at least, they know they have a fight on their hands. Biden is no longer standing by amid the slow-motion coup and white nationalist backlash now taking place.

“The way you have to heal, you have to recognise the extent of the wound,” he told reporters at the Capitol just after his speech. “This is serious stuff … You’ve gotta face it. That’s what great nations do, they face the truth, deal with it, and move on.”