The inauguration of Joe Biden as US president on 20 January has become a touchstone moment in the history of American democracy. Following the outrage of last week’s storming of Congress by Donald Trump supporters, at least 10,000 members of the national guard will be deployed in Washington by this weekend. Reports have detailed FBI warnings of possible armed protests in the capital and across the United States in the days ahead. The area around the Washington Monument, close to where Mr Trump urged supporters to “fight” for his right to stay in office, has been closed to the public. The mood is fearful, febrile and somewhat surreal. In the words of one newspaper headline: “Is this America?”

Since the foundation of the federal republic, the peaceful transition of power has been fundamental to America’s understanding of itself. In US democracy’s choreography, the presidential inauguration is designed as a moment of civic celebration that transcends partisan differences. That Mr Trump chose to mobilise an insurgency against the handover gives the measure of his narcissism, hubris and deranged will to power. Last week’s riot was not a one-off piece of performance theatre that got out of hand. The pitch for an assault on democracy had been rolled for months. In the autumn, speaking more like a mobster than a president, Mr Trump told the neo-fascist Proud Boys movement to “stand by”, and warned that the Democratic party would try to “steal” the election. Last week’s violent mayhem, which led to five deaths, was the culmination of a strategy to intimidate and discredit the democratic institutions of the country he leads.

Democrat members of the House of Representatives are therefore right to launch impeachment proceedings for a second time against a rogue president. As the charge sheet states, Mr Trump incited “violence against the government of the United States”. Assuming Wednesday’s vote to impeach is passed in the Democrat-controlled House, the next stage will take place in the Senate, currently in recess until after Mr Biden’s inauguration. A two-thirds supermajority would be required to convict, but it seems improbable that a sufficient number of Republicans will do the right thing. Another shaming moment looms for a party that has abased itself at Mr Trump’s feet in the pursuit of power and lost its soul in the process.

But even if legal process were to deliver Mr Trump his just deserts, the crisis of America’s growing polarisation – of which the president is a symptom as well as a cause – would remain. Tribalism has become a disabling virus in the US body politic, cracking the public square in two. Social media, belatedly under new scrutiny, is used by citizens to sustain alternate, conflicting realities: three in four Republican voters continue to believe that there was widespread voter fraud in November, despite the rulings of close to 100 judges to the contrary. As faith in the neutrality of public institutions declines, studies have shown a disturbing rise in the number of Americans – on both left and right – who believe that political violence is sometimes justified.

Against this dismal backdrop, the theme of Mr Biden’s inauguration speech will be “America united”. It seems likely that it will be delivered in the shadow of impeachment proceedings against his predecessor, and a mass military presence. This is a script that should belong to a bingeworthy drama on Netflix during lockdown. Instead, it is America’s dystopian reality. The new president’s healing message will be the right one. Making it heard will be the defining challenge of his long political career.