f this were a horror flick – and, Lord knows, these past four years have felt like one – we know what would come next. We’d be at that stage of the movie where the monster has apparently been slain, when the hero stands amid the rubble and the ruin consoling those who have survived, calm seemingly restored – only for the audience to gasp as the demon stirs back to life, rising from the dead to inflict one last blow. Joe Biden is certainly well cast as the steadying presence come to clean up the mess. But the fear persists that the villain who created it will return. Donald Trump threatened as much in his last public statement as president, uttering the chilling words: “We will be back in some form.” Given that Trump left the White House with his support among Republicans still at 82%, there is only one surefire way to ensure that never happens. Sixty-seven US senators – including 17 Republicans – will have to vote to convict Trump in his upcoming impeachment trial for inciting an insurrection on Capitol Hill on 6 January. If they do that, then Senate Democrats can vote by simple majority to ban Trump from ever holding public office again. (Think of it as Anne Archer shooting a resurrected Glenn Close at the end of Fatal Attraction.) That remains a possible denouement of the Trump saga, especially given the hints from Mitch McConnell, the Republican leader in the Senate, that he might vote to rid his party once and for all of Trump: this week he said that the former president – and what a pleasure it is to use those words – “provoked” the Capitol Hill mob. And yet, you wouldn’t bank on it. McConnell is now calling for the trial to be delayed, to allow Trump time to prepare. Given McConnell’s willingness to bend the Senate rulebook to his purposes, it’d be wise to start counting the spoons. Still, this might be to take the threat too narrowly, too literally even. What were Trump’s words? “In some form.” The monster might resurface in a new guise in 2024. In traditional Hollywood style, that would mean a sequel starring Son of Trump – or even Daughter – or it could mean someone from outside that desperate clan. This is, surely, the greater fear. That US nativist populism will find a new messenger, one free of the personal defects and grossness of Trump, one who has the quality that Trump lacked: the self-discipline to be a competent authoritarian. So often Trump’s autocratic impulses were thwarted not by the system but by his own ineptitude and the ineffectiveness of his fifth-rate team. What if next time the US – and the world – is not so lucky? To repel that as-yet-faceless threat will require deeper work than a simple vote in the Senate. And it will demand more than a mere return to the relative tranquillity of the Obama era. It will mean turning over the soil in which Trumpism grew, making it inhospitable to a new variety of that same, poisonous plant. This is the central challenge that now confronts President Biden. A first task is to dispel the question of legitimacy that hangs over his presidency in the minds of the one in three Americans who believe Trump’s big lie that he, not Biden, won the 2020 election. After the deadlocked election of 2000, a quarter of Americans did not accept George W Bush as the legitimate president, but that question mark faded in the smoke and dust of 9/11. In the absence of external attack, how can Biden persuade at least some of those recalcitrant voters to accept him as the country’s leader? Happily, the answer coincides with what is the most urgent problem facing him and the US. If Biden can make good on his promise to vaccinate 100 million Americans in 100 days, that in itself will be transformative. People’s lives will have changed in a direct and profound way, thanks in part to having Biden at the helm. In the process, he would have gone a long way to restoring Americans’ faith in the ability of government to do good. That is critical given that Trumpism was predicated on an insistence that democratic government is always feeble and useless, that it takes a strongman to get things done. The debate has been long and acrimonious over whether Trump supporters were drawn to him by “economic anxiety” or plain old racism, spiced with misogyny. But what if the answer contains elements of both? What if bigotry flourishes in unwatered earth? Biden’s $1.9tn rescue plan and an agenda of economic renewal may not win back the left-behind and eradicate Trumpism at a stroke – but it can’t hurt. Time, though, is desperately short. There is a curious cycle in US politics. In 1992, 2008 and 2020, Democratic presidents were elected alongside Democratic majorities in the House and Senate, granting them the muscle to implement their programmes. But for Bill Clinton and Barack Obama landslide reverses came within two years, depriving them of either one or both chambers of Congress thereafter. In other words, over a 12- or 16-year period Democrats usually get a squeezed two years to get things done. Biden’s majorities are much thinner than his predecessors’, and the clock is already ticking. The new president cannot allow himself to get bogged down in delay, tripped up by McConnell’s familiar tricks in the Senate. But that will take more than guile. The system that gives a rural, white Republican minority de facto veto power over the rest of the country – and note that the Democrats’ 50 senators represent a total of 41 million more voters than the Republican 50 – itself has to change. The wish list is long, from tackling voter suppression and gerrymandered districts to campaign-finance reform and abolition of a filibuster rule that demands 60 votes to get something through a 100-member body. Tackling all that will go against Joe Biden’s instincts. He is a creature of the Senate, faithful to its traditions. But as the columnist Ezra Klein puts it, for too long Democrats have “preferred the false peace of decorum to the true progress of democracy”. History suggests Biden will only get one shot. He must not throw it away – lest he revive the very spectre that gave him his chance. Jonathan Freedland is a Guardian columnist