Nine months after the election he comprehensively lost, the spectre of Donald Trump – darkly menacing, subversive and apparently immune from prosecution – continues to cast a shadow over US democracy and America’s global standing, distorting policy and poisoning political life. How can this be? Why is this horror movie still running?

Trumpism, like other fascist variants, is a disease, a blight – a noxious far-right populist-nationalist miasma that taints and rots all it touches. Older Europeans share a folk memory of fascism. But too many Americans just don’t get it. The will to stamp out this sickness before it returns in more virulent form is alarmingly lacking.

By refusing to confront his crooked predecessor and bring him to justice, Joe Biden feeds delusional Trump’s sense of godlike impunity, and the dread prospect of a blasphemous second coming. To a watching world, his paralysis smacks of weakness. It puzzles friends. It leads foes to hope that he, not Trump, is the blip.

Maybe Biden lacks the killer instinct. Yet you don’t have to be Niccolò Machiavelli to know Trump poses an existential threat to democratic norms. There will be no reciprocal forbearance, no forgiveness, if he gets a second chance, only vendettas, score-settling and ever greater abuse of power.

For now, Trump skulks at Mar-a-Lago, biding his time and endorsing loyalists for future contests. He claimed a success last week when an arch-sycophant won a congressional race in Ohio. He’s raising money – his war chest already totals over $100m. Polls show he remains easily the most popular presidential choice among Republican voters.

Stripped of its social media platforms, his spiteful voice does not carry as it once did – though he found space last week to attack “woke” women soccer players. But this relative quiet is deceptive. There’s a phoney war going on ahead of next year’s midterm election campaign – which Trump views as a warm-up for 2024.

Author Michael Wolff last month warned complacent Democrats that Trump was preparing for battle. “Trump [is] always ready to strike back harder than he has been struck, to blame anyone but himself, to take what he believes is his… Sound the alarm,” Wolff wrote. He said he was certain Trump would run again.

Who will cure this disease? Who can cleanse this blemish from the face of America? Disqualifying him as criminally unfit for public office is the obvious way to avert more West Wing mayhem. Yet “Gentleman Joe” and his fight-shy attorney general, Merrick Garland, keep pulling their punches.

What of the numerous counts of obstruction detailed by Robert Mueller’s Russia inquiry? No action by Garland’s justice department. What about multiple allegations of corruption and tax fraud? No federal prosecution in sight. Or a string of alleged sexual assaults? No criminal charges pending.

Asked what he would do about Trump’s crimes, Biden said last August that to pursue his predecessor in court would be “very unusual”. It was “not good for democracy to be talking about prosecuting former presidents”. In short, he’d prefer to ignore the problem.

Yet since he spoke, Trump has fomented insurrection – the 6 January assault on Congress – for which hundreds have been charged, though not he. He pushes his mendacious, destabilising “big steal” narrative. It has also emerged he pressured the justice department, as well as state officials, to discredit the election.

It’s not “good for democracy” to ignore blatantly unconstitutional wrongdoing by its highest office-holder. Doing so helps Trump dismiss everything as a hoax. It sets a dreadful political and ethical precedent at home. It damages America’s reputation abroad. But still Biden and Garland sit on their hands.

Trump blight is meanwhile taking a terrible toll. In deference to him and his base, it seems, cruel anti-migrant policies remain in place, progressive action on racial justice has stalled, and attacks on voting rights advance. The Republicans are now more cult than party.

This poisoning of the body politic extends overseas, too. Why, for example, should Tunisia’s president heed US homilies about democratic principles and the rule of law when they go undefended in America itself? Why should China? Why should anyone take Biden’s presidency seriously if the Maga champ can run rings around him from a Florida golf cart?

Iran vividly illustrates Trump’s malign influence at work. When he stupidly abandoned the 2015 nuclear pact, he empowered Tehran’s hardliners. Now they have seized Iran’s presidency, exploiting fears of Trump’s return. They warn the US cannot be trusted. It’s a message with legs.

The coddling of dictators from Moscow to Manila, the 2020 Taliban talks giveaway in Doha (which led directly to today’s Afghan meltdown), Jared Kushner’s Middle East peace-for-cash scam, and official denial of the climate crisis are all additional products of Trump blight. Biden struggles daily with the toxic fallout.

Some argue that Trump disease is exaggerated, that Biden’s bipartisanship is producing results – witness his new infrastructure plan. But if the impression takes hold that he cannot put his own house in order, the world – and American voters – will turn their backs on him.

Bottom line: the once and future king’s foreign fiascos continue to bedevil America abroad in the same way his corrosive contempt for democracy, law and common decency divides and debilitates it at home. Surely this situation cannot go on.

What other leader in the world would allow serial wrongdoing to go unpunished, would tolerate unceasing acts of subversion and disruption by so prominent and hostile a figure? If he wasn’t already dead, Machiavelli would die laughing.

Too-nice Joe must stop being polite, take the gloves off – and neutralise the Trump variant before it hits pandemic levels. Isolation and social distancing would help. So lock him up!