This week's Biden-Trump presidential debate could be the most significant in US history

The American commentariat is virtually unanimous that Thursday night’s first presidential election debate between US President Joe Biden and former president and convicted felon Donald Trump is potentially the most significant since the very first one held in 1960 between John F Kennedy and Richard Nixon. While these candidates are extremely well known to the public, both require a breakthrough moment in what has been a remarkably steady and even campaign. But if neither achieves a noteworthy success, or falls into one of the pitfalls yawning before them, it’s also possible that nothing will happen to significantly shift this race. There are several unique characteristics to this week’s debate . It will be the first between a sitting president and a former incumbent. It’s the first in decades to be handled purely by a single news organisation, CNN, rather than an independent national commission (which Trump has refused to work with). And it involves by far the oldest presumptive presidential candidates (both will be formally anointed at their party conventions next month) who are well over 75 (Mr Biden is 81 and Trump is 78). It’s also the earliest debate in any presidential election campaign, because Mr Biden is an essentially unchallenged incumbent and Trump was able to secure his party leadership with no effective opposition. The campaign is now in full swing, even though the conventions lie ahead, and in the run-up, Trump held a narrow lead nationally and in crucial swing states. However, as the campaign has gained pace and, especially, after Trump’s conviction on all 34 felony counts in the Manhattan adult film star hush money trial, Mr Biden has gained noticeable ground, and is now leading very narrowly in the most recent polls. But the campaign remains balanced on a knife edge. Neither candidate has clearly developed a winning coalition or decisive edge over the other, and both will be looking for a breakthrough moment of some sort. Trump, in particular, needs that. Despite his continued popularity among Republicans and gains among non-college educated African-American and Latino males , the momentum, such as it is, appears to be with the President, who also enjoys the distinct advantage of incumbency. But Trump, too, is running as a kind of incumbent, and the outcome probably boils down to which of the two unpopular and uninspiring men proves to be the dominant focus of attention. A de facto referendum on either candidate probably secures victory for the other. It’s no mystery that both candidates need to overcome negative assumptions about themselves. American voters are rarely moved by policy arguments, but rather respond to atmospherics, general impressions, likability and respectability. On both counts, each man must, above all, avoid pitfalls. Republicans have painted the President, who is undoubtedly showing his age, as senile and incompetent. If Mr Biden can repeat his performance at the State of the Union address in January, in which he looked engaged, fully competent and even sprightly, especially during rhetorical sparring with Republicans , he will probably have had a good night. It’s imperative that he does not come across as confused or bewildered, although voters may be patient with some rhetorical stumbling. Trump, by contrast, will have to control himself. He is more given to extreme rhetorical outbursts and excesses of outrage than he already was in the past, and if he comes across as overly aggressive, boorish and obnoxious – as he did in his debates with Mr Biden four years ago – he could sustain considerable damage. If, on the other hand, he is able to remain calm and controlled – and especially refuses to rise to the bait that Mr Biden certainly should be judiciously throwing at him or bristle at uncomfortable questions from the moderators – he could reassure voters that he’s not as unhinged as he often appears these days. He must also avoid the strange rambling that he appears to be increasingly given to at both public and, as widely reported, private appearances. The President will need to goad his opponent without unduly mocking or appearing to cynically provoke him. The former president must absorb these taunts, and incontrovertible facts such as his status as a convicted criminal, without appearing to lose control of his emotions or respond with transparently crude and preposterous lies. Trump continues to run as an outsider, even though he’s commanded a major party for almost a decade and served as president for four years. That presents him with the opportunity to continue to challenge the system, but if he appears ready to run roughshod over it or dismiss the Constitution when convenient, he will confirm many of the worst fears about his political evolution. Mr Biden, by contrast, will have to defend the constitutional system without seeming to apologise for structures that unduly advantage the few over the many. The debate provides a golden opportunity for the President to keep harping on a few key facts that can refute widespread misapprehensions that the economy under his leadership is in a recession (in fact, by most measures, it is exceptionally robust), or that crime is at unknown and rising highs (in the main, it isn’t). Trump has the opportunity to reinforce the nostalgia many voters appear to feel about his presidency and avoid being stung by reminders of the failures, particularly during the worst year of the Covid-19 pandemic, that contributed heavily to his defeat four years ago. And he’s certainly going to have to resist relitigating the 2020 election or harping on conspiracy theories that few swing voters believe and fewer still consider relevant to the next four years. But most of all, both men must avoid significantly reinforcing the stereotypes that haunt them: that Mr Biden is a virtually senile servant of an unjust status quo, and that Trump is a mentally unstable would-be authoritarian. Atmospherics and general impressions will be key. If either man strongly reinforces these impressions, it could be disastrous. But if both avoid the pitfalls, little may change. Nonetheless, this has all the makings of one of the most consequential presidential debates in US history. Anyone interested in US politics must watch it carefully. But remember: style will prevail over substance, and general impressions or breakthrough moments will, as always, carry the day.