Donald Trump hectored and interrupted Joe Biden nearly every time he spoke and the former vice president denounced the president as a "clown" and told him to "shut up."

In a chaotic, 90-minute back-and-forth, the two major party nominees expressed a level of acrid contempt for each other unheard-of in modern American politics.

Four years ago, during the 2016 presidential election, Joe Biden was asked if he wished he could debate Donald Trump. He responded: "I wish I were in high school, I could take him behind the gym."

But last night he finally got his chance: 90 minutes with his arch-nemesis. Biden has clearly got under Trump's skin: the president has recently been claiming that the Democratic candidate takes performance-enhancing drugs to improve his debating skills.

Each candidate had different aims last night. Trump's popularity has been sinking thanks to the Covid-19 pandemic and the economic damage that it has caused to the US economy.

This week he has been rocked by revelations, released by the New York TimesOne of the most prestigious newspapers in the USA and in the world. It has won 130 Pulitzer Prizes, more than any other newspaper. It has frequently been in conflict with Trump, who routinely refers to it as "The Failing New York Times"., that he only paid $750 in income tax in the first year of his presidency. The debate provided an opportunity to turn his campaign around.

Biden has a healthy lead in the opinion polls, so his job was much easier. All he had to do was defend himself from Trump's attacks, and avoid any gaffes of his own.

But he has not made many public appearances in the last few months, and there was a danger that he would wilt in front of renewed scrutiny.

Biden, at 77, would be the oldest man ever to win the presidency, and some have questioned whether he is still mentally fit to take on the top job. And 74-year-old Trump has also faced questions about his mental abilities.

In the end, however, any concerns about either candidate's mental health was not an obvious issue.

The debate focused on seven topics: the Supreme CourtThe highest court within the hierarchy of courts in most legal jurisdictions., Covid-19, the economy, race relations and violence, the candidates' records, climate change and the legitimacy of the election.

It quickly descended into chaos, with Trump constantly shouting over Biden - he interrupted Biden 73 times - and Biden responding with frustrated insults.

Trump tried to paint Biden as a weak leader, insisting that if the Democrat wins the election, he will come under the control of the socialist wing of his party. He tried to distract Biden with constant interruptions.

Biden focused on the question of Trump's competence, repeatedly accusing the president of lacking a plan for reforming healthcare and dealing with Covid-19. He addressed the audience directly several times, presenting himself as the voice of ordinary people.

Some attacks were simply surreal. Late in the night, Trump claimed that Biden's climate change plan wanted to "take out the cows".

Towards the end of the debate, Trump once again cast doubt on the legitimacy of the election, insisting that some votes for him were being deliberately thrown away.

Biden pushed back firmly on these claims, but the matter has further stoked fears that Trump might refuse to accept the result.

Yes, say some. They point out that roughly one hundred million people will have watched last night's debate, including undecided voters. The pandemic has restricted campaigning, so for many this would have been the first chance to hear the arguments. It also gave them a unique chance to assess the candidates and their ability to handle pressure.

No, say others. There is very little evidence that debates actually change people's minds, especially when they are as scrappy and inconclusive as last night's. Both candidates have been in the public eye for decades, Biden as a senator and then vice-president; Trump as a reality TV star and then, for the last four years, president: most voters have already made up their minds about them.