Joe Biden has been here before. Not necessarily this exact spot — a drab shopfront in a strip mall in south Des Moines brightened only slightly by the red, white and blue of Biden 2020 regalia — but here, in Iowa, trying to persuade voters that he should be the next president of the United States. He enters the campaign office as you’d expect a former vice-president to arrive: late, after his aides have fussed around the room for half an hour, and to the shkshkshk of a dozen camera shutters. The 78-year-old is slim and smartly dressed, handsome with neat features, blue eyes and a telegenic smile. 

He looks old, but the right kind of old; the kind of old that a septuagenarian man might pick out of a plastic surgeon’s catalogue. Indeed, there is some speculation about how exactly Biden’s face got so taut and tidy. 

He proceeds to do all the things Joe Biden has been doing for years. He flits from the light-hearted to the serious and back again, cracking dad jokes with the young volunteers assembled for this photo-op one minute and giving them earnest old-timey advice the next. “My Dad always said showing up is half of winning,” he tells them. The schtick is equal parts global statesman and avuncular Irish-American cheekiness. The effect is more ex-presidential than presidential — and the mood is flat.

It’s more than 30 years since Biden first came as a presidential candidate to this all-important state, which kicks off the Democratic party’s nominating process. That bid came to an abrupt end when Biden was forced to resign for, among other things, the unlikely crime of plagiarising a Neil Kinnock speech. He tried again in 2008, winning just one per cent of the vote in Iowa before being picked as Barack Obama’s running mate. This time is different. Three election cycles on, after eight years as the right-hand man to the most popular figure in Democratic politics has boosted his standing and four years of President Trump has worn half of the country out, Biden thinks he is the reassuring figure this moment demands. 

In 1987, Biden positioned himself as the liberal heir to Bobby Kennedy. This time, he’s a walking reset button, he’s the “we’re better than this” candidate, the “can’t we just go back to the way things were?” candidate. And, with a lead in the average of national polls ever since he announced his candidacy a year ago, he’s the front-runner. 

Other than reassurance and nostalgia for a time before Trump, Biden is selling — well, salesmanship. While his Democratic rivals hawk bold policies and elaborate plans, he has startlingly little to say about what he might actually do in office. Instead, this twice-failed presidential candidate wants to persuade you of one thing: that he can win. The problem is that there is plenty to suggest he might not. In the monthly televised debates, his contributions have been rambling and sometimes incoherent, enlivened only by the prospect of an imminent slip up from the self-confessed “gaffe machine”. This is not a helpful attribute for a steady-hand-on-the-tiller candidate like Biden. Nor is the entanglement of his son’s business in Ukraine with the messy impeachment trial that dominates headlines even if it scarcely gets mentioned on the campaign trail. Democratic strategists and voters also worry Biden might not have the stamina for the gruelling path to the White House, let alone the job itself. In conversations with dozens of Iowa voters three weeks before caucus day, I keep hearing the same thing: “I love Joe, but . . . ” One  Iowan even described Biden as her “favourite politician of all time”, but won’t support him. Some are more explicit: “He’s too old!” says one exasperated citizen.

But it isn’t just the self-evident shortcomings of Biden the candidate that undermine the case for his nomination. Also working against him is something bigger, something that goes to the heart of American politics. It’s the slippery question of which of the old rules still apply after Trump broke so many of them in 2016, and a lack of confidence in what “electability” really means in 2020. 

At the Des Moines campaign office Biden ends his speech not in the rhetorical crescendo you might expect from a seasoned campaigner but with a slightly underwhelming promise that “if I’m the nominee, I will not let you down.” Volunteers applause politely. He ignores questions from reporters and exits through a door with a campaign poster affixed to it that reads “No Malarkey.” 

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When the younger Biden first asked Iowans for their support, Bernie Sanders was making a name for himself as the unapologetically socialist mayor of Burlington, a small progressive college town in Vermont. Elizabeth Warren was a legal scholar at the University of Pennsylvania specialising in bankruptcy law — and still a Republican. Pete Buttigieg was a five-year-old boy in South Bend, Indiana, the town he would go on to lead as a wunderkind mayor. 

Thirty-three years later, these four Americans are all looking for the same thing: an Iowan seal of approval. As we go to press, with caucus day in under two weeks, pollsters agree that the Iowa race is close. Too close, in fact, to be sure of very much beyond the identity of the four candidates with a reasonable chance of winning.

If Biden comes out on top here, and in other early states, where he was originally expected to underperform his level of national support, then he could have half a hand on the nomination remarkably early, killing off the hopes of his rivals in Iowa and stopping late entrant Mike Bloomberg (who is focusing on later states) in his tracks. 

If Sanders triumphs, he emerges as the undisputed alternative to Biden, turning things into a two-horse race. Both Warren and Buttigieg need a strong showing to keep pace. If anyone outside this top four wants to be taken seriously much longer then they probably need to crack the 15 per cent threshold needed to win Iowan delegates. 

I meet enthusiastic supporters of all of them. Out-and-out Bernie Bros at a debate watch party in downtown Des Moines, a retired women in a cap dotted with Buttigieg badges at a rally on a bitterly cold night in the north of this snowbound state, students energised by Elizabeth Warren’s bevy of plans to overhaul American capitalism. 

But the person who looms largest at all of these events is Donald Trump. A debate over who is best placed to win the national contest is part of any primary process, but the extent to which Trump dominates proceedings is exceptional — and no candidate will get very far with these voters unless they can convince them of his or her ability to boot him out of office. 

At least superficially, Sanders is the candidate with the biggest electability problem. An independent senator from Vermont, he has trodden a lonely path to the top of American politics, building a devoted following along the way. However energetic his base, self-described democratic socialists have not fared well in US presidential elections and, were he to win in November, Sanders would be comfortably the most left-wing president in American history. 

This cycle, his flagship policy is Medicare for All, an overhaul of America’s healthcare system that may address an area of genuine concern for voters but is riddled with electoral difficulties. Instituting a single-payer system means huge tax hikes on middle-class households and the elimination of existing healthcare plans. 

Then there is the age problem — Sanders is as old as Biden, even if his performances, both on camera and in person, are considerably more energetic. He suffered a heart attack in October and was forced to take a break from the campaign trail in which most people assumed his presidential bid would soon fizzle out. Oddly, however, his comeback from that medical setback proved to be an energising moment — he raised a whopping $34.5 million in the fourth quarter of 2019 from nearly two million individual donors — and Sanders has looked like Biden’s most serious rival ever since. 

The hazards for the Sanders campaign are hard to ignore at a small gathering of his supporters at the University of Iowa. The 50-odd people were there not to hear from the candidate himself, but campaign surrogates. Cornel West is a long-standing Sanders supporter and a familiar face on the American left. A prominent black public intellectual, philosopher and Harvard professor, the 66-year-old is a merciless critic of Barack Obama and everything else that looks like moderation in the Democratic party. He has preached a socialist creed, invoking the intellectual inheritance of Martin Luther King to do so, for decades. 

In his trademark black tie and waistcoat, he delivers a barnstorming, culturally rich endorsement of the Vermont senator that has the students and locals fired up on this cold January morning. “Bernie Sanders is a tender brother, he’s a kind brother, he listens to everyday people,” he tells them. “Electability” doesn’t come into it. Bernie is a thermostat, not a thermometer, he says. “Don’t let anybody tell you, ‘Oh my God, he is a democratic socialist, America is going to look like the Soviet Union in four years’,” he warns. “No — you tell them: Get off the crack pipe!”

Attendees are just as unequivocal in their support: “I was a big Bernie fan four years ago, and I’ve followed him for 30 years,” says one. “He’s the most consistent candidate, he’s the one honest candidate and I agree with every single one of his policies.” Others compare notes on how far they have driven for the event. A middle-aged man sporting a “Bernie 2020” T-shirt over his sizeable gut proudly announces that he has moved to the state to help get Sanders elected. 

It all feels a lot like a Corbyn rally. And to many Democrats, the abject failure of Labour in last year’s British election is a powerful reminder not to confuse the enthusiasm of Sanders’s loyal support with the ability to win a national election. However, if Democratic moderates have the cautionary tale of Corbyn’s failure in 2019, the left can point to Hillary Clinton in 2016. You don’t need to share Sanders’s politics to see that third-way triangulation hasn’t proved especially successful in recent years. While a candidate with a radical agenda needs to explain why he won’t bomb at the ballot box, a centre-left insider nee ds to accept that the last two presidents won the White House as insurgent outsiders and demonstrate why this time is different. 

The authors of an essay in Jacobin, the pro-Sanders house magazine of American millennial socialism, frame the far-left case for electability as follows: “While every other general election matchup seems likely to descend into the bleak and muddled culture clash of 2016, a contest between Sanders and Trump would present American voters with a stark choice: the populist who wants to win you healthcare and cancel your debt, or the rich prick who doesn’t care if you live or you die so long as your boss gets paid.” 

Sanders is the closest thing the Democrats have to a Trump of their own: a straight-talking candidate committed to radical change and overturning conventional wisdom, and with enduring popularity that frustrates the party establishment. His candidacy is doomed for all the reasons Trump’s election bid was a non-starter. We all know how that story ended. 

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If Biden has pitched himself as the most explicitly “stop Trump” candidate, and Sanders is a kind of mirror image of the president, then Pete Buttigieg is standing on a cleverly constructed “tough on Trump, tough on the causes of Trump” platform. 

The 38-year-old has a stump speech that varies a little from event to event, but every time I hear it in Iowa it starts with an invitation to the audience to imagine “a day in our future that I hope is not very far off” and that is “the first day the sun comes up over Mason City [or Clear Lake or whichever Iowa town he happens to be in], over America, and Donald Trump is no longer president of the United States.” It’s a line that always gets a big cheer, before Buttigieg goes on to say that “the reason I always ask folks to picture that day is because it’s not the day our troubles end but the day our work begins.” Whoever is in charge on that day is going to need to unify the country, he argues, and also “deliver big answers to big problems, because the problems that got us to this point are only going to get more serious each passing day between now and then”.

Buttigieg has a CV that ticks all the boxes: a midwestern Rhodes scholar who served in Afghanistan and former mayor of the kind of hollowed-out town where Trump’s message of economic decline really resonates. He’s also the first openly gay candidate to seek the Democratic nomination. He speaks with a self-assurance and thoughtfulness that would make for an interesting foil to Trump’s braggadocio in a general election campaign. At his rallies I meet former Republicans who no longer recognise the party they once supported, a twentysomething who lost his job because of Trump’s steel tariffs and college students turned off by the leftwards drift of some of the other candidates. At one event, he even piques the interest of a voter in a “Trump 2020” baseball cap. 

While Mayor Pete (as he is universally known) polls well in midwestern states like Iowa, his nationwide numbers are less impressive, not least because of a well-documented problem with black voters. In many ways, Buttigieg’s platform screams “electable”. He has heeded caution in the face of a progressive wing convinced that now is the time for a raft of radical policies like Medicare for All and a Green New Deal, but without the passion of the left-wing candidates or the reassuring experience of his moderate rivals, his candidacy can surely only go so far. 

While I am in Iowa, an uneasy truce between Sanders and Warren, the next most left-wing candidate, comes to an abrupt end when it emerges (almost certainly from the Warren camp) that in a private 2018 meeting between the two candidates Sanders is alleged to have expressed concern that a woman couldn’t win the presidency in 2020. Immediately after a CNN debate in Des Moines in which Sanders denied the story, Warren is caught on a hot mic telling her longtime senate colleague, “I think you called me a liar on national TV.” 

Warren’s candidacy is built on a wonky brand of populism that promises to rewire the American economy and redistribute power away from a coterie of corporate bogeymen. Her professorial tone and her CV — teacher, legal scholar, creator of the Consumer Financial Protection Bureau in the wake of the financial crisis, and liberal Massachusetts senator — means the message, however ill-advised, is delivered with considerable authority. She has effervescence and enthusiasm that mean she is the one septuagenarian in the race whose mental and physical fitness for office is unquestioned. As with Sanders, she would be the most left-wing president in living memory. Unlike the other populist options available, her message seems to resonate most with the liberal cultural and academic elite; the risk is that she would pile up votes in parts of the country where they aren’t necessarily needed, but has limited appeal in the parts of the country that will prove decisive in November. 

The row between Sanders and Warren about gender is revealing not because it demonstrates any kind of misogyny in the Vermont senator — even if the Warren campaign does little to dissuade people of that notion. Rather, it is yet more evidence of the way in which 2016 has scrambled old certainties. Gone is the yes-she-can glass-ceiling-smashing swagger with which Hillary Clinton launched her 2016 campaign. Some might want to double down on left-wing identity politics and fight a high-stakes, no-holds-barred culture war with Trump. Others aren’t so sure.

At a warren event in Indianola, a small town south of Des Moines, a voter tells me he is torn between Warren, Sanders and Biden. Like most of the people I speak to, he says he is looking first and foremost for a candidate who can beat Trump. They need the “character, appearance and attitude that will make that happen”, he says. “Warren is old enough, she’s had enough diverse experience, she can speak without hesitation and touch on all the aspects of the job, but I wonder if the voters are willing to elect a woman.” 

This is an uneasy moment in American politics. Iowans, like voters in other states, find themselves second-guessing their own convictions, unsure of the country’s appetite for radical change and uneasy about their neighbour’s possible prejudices. Almost all of this is thanks to Trump. And perhaps the real lesson for Democrats from 2016 is to avoid the meta-conversation about electability that preoccupied so many people in Iowa. After this electability-obsessed caucus we may see that those who fare the best are the ones who, rather than overthinking what it is the voters want, appear most comfortable in their own skin. And, for all their unmissable shortcomings and undeniable differences, the two candidates who seem most authentically themselves are Joe Biden and Bernie Sanders.