Joe Biden is a candidate whose performance on the stump ranges from badly flawed to awful. He is a meandering, unfocused speaker, often unable to complete a sentence, let alone a thought, with a record in office that is decidedly patchy, marred by several past positions he struggles to defend. And yet Biden is now the frontrunner for his party’s nomination to take on Donald Trump. What’s more, the current mood, and specifically the threat of coronavirus, might just turn his defining weakness into a strength – and give him a serious shot at the White House.

I saw his limitations for myself last month in Hudson, New Hampshire, as he paced around a high school gymnasium delivering a rambling monologue that suggested a politician well past his prime. Stronger on autobiography than policy, he strung together childhood memories, mottos taught him by his father and a kind of perplexed outrage that Trump’s America was not a country he recognised any more: “What’s this all about?” he asked, as if befuddled. “What do we stand for?” In New Hampshire, he finished fifth.

Yet in the last seven days Biden has staged what is surely the most remarkable turnaround in modern US political history, a massive win in South Carolina setting off a chain reaction that brought victories across the south and midwest on Super Tuesday. Only Bernie Sanders now stands between Joe Biden and the nomination, with the map of upcoming primary contests tilted in the latter’s favour.

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Sanders likes to say it was the “political and corporate establishment” that handed victory to Biden, but that’s a stretch. For one thing, the Biden campaign was all but broke going into Super Tuesday, outspent by Sanders by a ratio of seven-to-one (and outspent by Mike Bloomberg by 100-to-1). Biden had only a skeletal presence on the ground, dwarfed by Sanders’ vast grassroots operation. Besides, it was not the establishment that turned out for Biden, but African-American voters – the most consistently faithful group within the Democratic coalition – who backed him over Sanders by huge, crushing margins. Along with suburban women, it was black America, not corporate America, that made the difference.

There are plenty of lessons here. One is that money and organisation are not the decisive factors they were assumed to be: just ask Bloomberg, who spent $500m and won not a single state, while Biden won states he didn’t even visit. Another is that sexism and its offshoot - second-guessing other people’s sexism - pervades US politics. Elizabeth Warren was the smartest candidate in the Democratic field, the most accomplished debater and may well have made the best president, but she could not make headway. I saw part of the explanation for myself in New Hampshire, speaking to countless women who admired Warren enormously, and were desperate to see a woman in the White House, but who had ruefully concluded that their fellow citizens were just not “ready” to make that happen. They had seen how misogynistic unease with an older, opinionated woman had proved fatal to Hillary Clinton in 2016 and they were not prepared to risk a repeat of that in 2020. So they voted vote for a man instead.

One aspect of the Biden resurrection was foretold, contained within the very structure of this race. Polls have consistently shown that while Sanders could command between 25% and 30% of Democratic voters, a clear majority were either anti- or non-Sanders voters. The trouble was, for a whole year and until this week, that non-Sanders majority had at least five faces. After South Carolina, once Pete Buttigieg and Amy Klobuchar had dropped out, it began to have fewer, and eventually just one. Once the non-Sanders camp was unfragmented, it could start winning.

Perhaps inevitably, the face it chose was a familiar one, belonging to a man whom Democrats feel they’ve known for ever, whom most of them trust and like. Even the voters I met who were not backing Joe Biden described him the same way: as a “good man”, as a “really decent person”, as someone of warmth and “empathy”. Americans know the losses he has endured. His first wife and daughter were killed in a car crash when Biden was 30; his eldest son, Beau, died of cancer aged 46. Biden’s best moments in Hudson came as he listened to people talk of the pain they had endured. “Like most of you, I’ve lost a lot in my lifetime,” he said. “But I’ll be damned if I’m going to stand by and lose my country.” That ability to show basic human empathy could count in a country that is currently fearful, even bracing itself for disaster.

Biden is remembered as the number two in the most unflappably efficient administration most Americans have ever known

Which brings us to the coronavirus. For four decades, the US right has had great success in persuading voters that government is the problem, not the solution. That’s found its most extreme form in Trump, elected on an implicit pledge to shake the whole thing up, if not burn it all down. He’s gutted government departments and run down federal agencies, left posts vacant or filled them with pals, cheered on by a base that for years has heard the fire-breathers of Fox News and talk radio cast “government bureaucrats” as the enemy.

But how does such talk sound now, when people are trembling at the prospect of a pandemic? In a moment like this, people don’t turn against government, they turn to it. In good times, you might get applause railing against “federal officials” or “elite experts”. In a crisis, those are precisely the people with the authority to get a grip and offer reassurance.

Suddenly, Biden’s 50 years as a Washington insider can be presented less as a liability than an asset, because that’s half a century of valuable experience. Better still, Biden is remembered as the number two in the most unflappably efficient administration most Americans have ever known, namely the one headed by Barack Obama. The fact that Obama chose Biden as his deputy has meant that, even without making an explicit endorsement, Obama has long served as Biden’s chief character witness. Now that line on the résumé counts for even more, with Biden’s presence in the team that presided over an economic recovery and governed with stability and calm – “No drama Obama” they called it – a prime credential.

That will help Biden if he faces Trump, but it could also ensure he does. For Bernie Sanders’ brand is not one of steady calm so much as upheaval and “revolution”. That thrills his most devoted supporters but, Tuesday’s results suggest, it scares off those who yearn for stability. (At a crucial moment a fortnight ago, after he’d won in Nevada, Sanders could have moved to assuage those fears; instead he reinforced them, defending his past praise for the record of Fidel Castro.)

At any other time, Biden’s age, manner and CV could have doomed his candidacy. But with a plague looming, Americans might just view a flawed man of undoubted empathy and with an intimate knowledge of loss, a man who’s spent a lifetime inside the US government, as something like a remedy.

• Jonathan Freedland is a Guardian columnist