o contemplate the impact of Donald Trump losing next month, it helps to imagine him winning. The impact on the United States of a second Trump term would be transformative, of course, but I’m thinking of the effect on the wider world and, in particular, on the politics of Britain. So picture, for just a moment, what a second against-the-odds Trump win would mean for this country. A Tory party that has made Brexit its defining mission – and insists it views a no-deal crash-out from the EU “with high hearts and complete confidence”, as Boris Johnson put it today – would be boosted by the message that populist nationalism was not a 2016 aberration but rather a global movement with enough juice to endure into the mid-2020s. The Illiberal International embodied by Viktor Orbán, Jair Bolsonaro and Vladimir Putin would draw strength from an unexpected victory for its most senior member; and, although Johnson does not like to put himself in that company, he and his Brexit government would be lifted by US confirmation that the spirit of the age is not international co-operation but a world of competing states, each dedicated to making itself great again. Now consider the reverse. Defeat for Trump would signal that the populist fever had broken, that the 2016 nationalist sweat was starting to cool. As others have argued, with Trump gone, Johnson would look beached and alone, wearing a costume suddenly out of style. What’s more, if Americans repudiate Trump, that would suggest the reassertion of a political rule that seemed to have been shredded in 2016: that there are some things voters will not tolerate. That incompetence, corruption and dishonesty exact a price. The restoration of that standard would not be kind to Johnson. And a defeated Trump would rob the prime minister of what has been a useful, if largely unspoken, argument: no matter how bad Johnson has been, no matter how inept his handling of the pandemic, at least he’s not been as awful as that man in the White House. If Trump is beaten, that handy comparator will become unavailable – along with the relative reassurance it provided. Naturally, if a Trump defeat is bad for the Tories, a Joe Biden win is good for Labour. Party bigwigs are wary of getting ahead of themselves on that score, and not only because, after the trauma of 2016, no one is taking anything for granted. They’re also mindful of the temptation – and danger – of reading a Trump defeat as proof that the last four years was a blip, a cue to return to the comforting warmth of the old normal. As one former cabinet minister puts it, such complacency would overlook the fact that “Normal politics was clearly failing because we ended up with Trump” (and, you might add, Brexit). There’s another caveat, too, besides the obvious fact that Britain and the US are very different countries. Biden is not in the same position as Keir Starmer. Coming off a crushing defeat in 2019, the Labour leader’s first task has been to persuade the electorate that he represents a complete break from his predecessor. Not for nothing is his slogan “New leadership”. Biden has been making the reverse move, reminding voters at every opportunity of the recent Democratic past and his role in it, deputising for a president, Barack Obama, whose stock climbs ever higher. Even so, the effect of a Biden win on Labour and Starmer would be enormous. Part of it comes down to the fact that, for all its multiple dysfunctionalities, the US still operates as a global trendsetter, so that a lead set there is often followed elsewhere. More specifically, a President Biden would confirm that a candidate who is unexciting but capable and conspicuously decent can win – especially during a crisis. If that becomes the template for leadership, then it’s one that fits Starmer well – and Johnson very badly. Of course, what holds true of this political moment may no longer apply by the time Starmer fights a general election in 2024. With any luck, the pandemic will be a distant memory by then. Intriguingly, every Labour figure I spoke to took it as read that Johnson will not be the opponent Starmer faces: they assume that he will be gone. They reckon Johnson hates doing the job and is only waiting for a high note on which to bow out – though those may be in short supply for quite a while. Either way, those Labour bigwigs strongly doubt that Starmer will have Biden’s advantage in competing against a shameless fraud who has so demonstrably failed to manage a national crisis. All the same, a Biden victory would offer encouragement to Starmer and his approach. For Biden has been at pains to stick to a bread-and-butter message of jobs and healthcare, and not to be diverted into culture-war battles against the right. Time after time, he has refused to take the bait dangled by Trump. The Democrats’ TV ads rarely mention whichever atrocity or insult has just come out of Trump’s mouth, staying focused instead on the issues that matter to voters. As Biden said in their TV debate, addressing the audience after Trump had attacked Biden’s son: “This is not about my family or his family. It’s about your family.” So far it seems to be working – handily for Starmer who, with his refusal to play the Captain Woke role assigned to him by Tory HQ, has adopted the same tactic. If Biden were to lose, the chorus from the Democratic left will be loud and vociferous: Biden was too mild, too centrist, too modest in his ambition. They will be adamant that a radical voice, like that of Bernie Sanders, would have won the votes to eject Trump from the White House. If Biden loses, that argument will echo across the Atlantic, as the British left urges Starmer to learn the obvious lesson: abandon caution and turn left. But surely that means the reverse must apply if Biden wins. He will have prevailed by appealing to the broadest possible coalition of voters – and not only by not being Donald Trump. The polls show, yes, dreadful numbers for the president, but also that Biden’s ratings have steadily gone up as the campaign has gone on. Even back in 2019, his poll lead over Trump was larger than that enjoyed by the likes of Sanders and Elizabeth Warren. So this is not only a negative verdict against Trump, though that’s part of it: there’s also good evidence that Americans warm to Biden and the kind of politics he embodies. It may not fare well on Twitter, but a message that combines reform, patriotism and reassurance, rather than ideological fervour, seems to appeal. That said, Starmer should be careful to take one more bit of advice from Biden. The Democrat has worked hard to unite all wings of his party, to ensure Sanders and Alexandria Ocasio-Cortez are on side as well as Obama and Hillary Clinton. If Biden wins, that too will be a valuable lesson for Labour. But let’s not get carried away: it’s still an if. Jonathan Freedland is a Guardian columnist A panel of Guardian journalists will discuss the US election at a Guardian Live online event on Tuesday 20 October, 7pm GMT (2pm EST) Book tickets here