Cleveland will see US President Donald Trump and former vice-president Joe Biden go head to head for the first time on the same stage, amid a bitterly acrimonious campaign in a dangerously divided United States.

The first of three presidential debates - at 9am tomorrow Singapore time - will be a challenge principally for Mr Biden. While he is consistently, if narrowly, leading in national polls, Mr Biden is pitching himself as the anti-Trump, who will bring decency, compassion and unity back to America.

But he also faces accusations of being weak and uninspiring. He has staged far fewer in-person campaign events than Mr Trump.

He also faces a President skilled in the arts of bludgeoning rivals and playing to the gallery of his own narrow but devoted base.

Mr Biden is likely to be the target of well-aimed barbs over the conduct of his son, Hunter Biden, who is alleged to have benefited from his father being vice-president.

The flip side is that expectations of Mr Biden are relatively low, so a passable performance will impress.

Also, he comes into the debate on the heels of potentially damaging revelations, in an apparently extensively researched New York Times article, that Mr Trump has been paying startlingly low income tax on his family business empire.

The President, while deflecting blame to China, is also vulnerable on his pandemic record; last week, America passed the grim milestone of 200,000 deaths.

Unlike Mr Trump, who considers his almost daily prickly exchanges with reporters as adequate training, Mr Biden has been preparing extensively for the debates. After Ohio, they will meet in Florida on Oct 15 and in Tennessee on Oct 22.

"President Trump will definitely try to throw the (former) vice-president a bunch of curveballs that are designed to get him off his game," Mr Jay Carney, who was Mr Biden's communications director and also White House press secretary under president Barack Obama, told Bloomberg News.

"(Mr Biden) fully expects and is preparing for that and knows that taking that bait is not what he wants to do," he said.

Earlier this month at a fund-raiser, Mr Biden said: "I hope I don't get baited into getting into a brawl with this guy." He added: "It's going to be hard, because I predict he's going to be shouting."

Last Saturday, Mr Biden told MSNBC that Mr Trump "doesn't know how to debate the facts. He's not that smart. He doesn't know that many facts. He doesn't know much about foreign policy. He doesn't know much about domestic policy. He doesn't know much about the detail".

In an average of national polls maintained by the political analysis website FiveThirtyEight, Mr Biden has a roughly seven-point, 50.3 per cent to 43 per cent, lead over Mr Trump.

But six states - Florida, Georgia, North Carolina, Arizona, Wisconsin and Ohio - are considered toss-ups, which is alarming for Mr Biden as it indicates that Mr Trump could repeat his 2016 triumph, in which he lost the popular vote but won a handful of key states to win the all-important Electoral College.

The 90-minute debate at Case Western Reserve University and Cleveland Clinic will be moderated by Fox News host Chris Wallace.

The topics, each of which will get about 15 minutes, are Mr Trump's and Mr Biden's records; the Supreme Court; the handling of the Covid-19 pandemic; the economy, race and violence in American cities; and the integrity of the presidential election.

An obvious omission, climate change, will almost certainly figure in subsequent debates.

The issue of the Supreme Court has been thrown into sharp focus with the death of Justice Ruth Bader Ginsburg, an icon for liberals and the left, and Mr Trump's nomination last week of Judge Amy Coney Barrett, a darling of religious conservatives, to fill the vacancy.

He is intent on Mrs Barrett's confirmation before the election to cement what would then be a principal domestic legacy - packing the court with conservatives.

The last topic is also fraught, and not unconnected with the push to fill the seat left vacant by Justice Ginsburg.

Many analysts see America barrelling towards a constitutional crisis and possible violence if, as seems likely, the result of the election is either muddied by a long, drawn-out process involving court battles, or simply not accepted by one or the other candidate.

Mr Trump has repeatedly and explicitly questioned the integrity of mail-in ballots, which have always been a feature of American elections - in some states more than others - and in this election assume greater importance given the risk of mingling in queues and groups in the midst of the pandemic.

He has stated more than once that the only way he can lose is if the election is "rigged".

Like heavyweight wrestling matches, the presidential debates are part of the showbiz of American politics, an ecosystem in which Mr Trump, a former reality television star, thrives.

As a long-time senator and a veteran of the Barack Obama campaigns, Mr Biden's experience of debates is very substantial - but more traditional.

"Debates don't reward folks who speak in complete sentences and long paragraphs," Mr Carney said.

"They really reward one-liners and insults and zingers."