President Donald Trump and his challenger Joe Biden have fiercely clashed in one of the most chaotic and rancorous White House debates in years.

Amid angry shouting and name-calling, the two fought over the pandemic, white supremacy and the economy during the 90-minute forum in Cleveland, Ohio.

Mr. Biden called the president a "clown" and told him to "shut up". Mr. Trump brought up drug use by his rival's son.

Opinion polls suggest Mr. Biden has a steady single-digit lead over Mr. Trump.

But with 35 days until election day, surveys from several important states show a closer contest.

Polls also suggest one in 10 Americans have yet to make up their mind who to vote for. But analysts said Tuesday night's debate - the first of three - probably would not make much difference.

What were the key moments?

Overall, the debate was light on policy, with little serious discussion or argument over what either candidate would do while in office.

The tenor became clear early on, as the two candidates sparred over healthcare. Frequent interruptions from Mr. Trump saw Mr. Biden call the president a "clown".

As they moved on to the Supreme Court, the rancour continued, with Mr. Biden refusing to answer when asked if he would try to expand the number of judges.

"Will you shut up, man?" the Democratic candidate snapped, later adding: "Keep yapping, man."

Mr. Trump, the Republican candidate seeking a second term, responded: "The people understand, Joe. 47 years [in politics], you've done nothing. They understand.

In one of the most talked about exchanges of the night, the president was asked by the moderator, Fox News anchor Chris Wallace, if he was prepared to condemn white supremacists.

He initially said he would, but when asked to denounce the far-right Proud Boys group by name, he sidestepped.

Mr Trump said: "Proud Boys, stand back and stand by, but I'll tell you what, somebody's got to do something about antifa and the left."

The Proud Boys, an anti-immigrant, all-male group, took to social media to celebrate. "Standing down and standing by sir," it posted on Telegram.

Earlier, Mr Biden said: "This is a president who has used everything as a dog whistle to try to generate racist hatred, racist division."

In other moments:

• At one point, the insults became deeply personal when Mr Trump suggested Hunter Biden, the Democrat's son, had been thrown out of the military for cocaine use. Mr Biden said his son "had a drug problem" but had "fixed it"

• Mr Trump was asked if he would encourage his supporters to be peaceful if results of the election were unclear. "I'm encouraging my supporters to go into the polls and watch very carefully," he responded

• When Mr Trump claimed Mr Biden would be at the behest of the left of the Democratic Party over health and environmental policy, Mr Biden responded: "I am the Democratic Party right now"

• Mr Trump defended his effort to swiftly fill a US Supreme Court seat to cement a 6-3 conservative majority on the bench, saying: "We won the election and we have the right to do it"

What did they say about coronavirus?

Mr Biden said Mr Trump had "panicked" over the coronavirus pandemic, which has killed more than 200,000 Americans.

"A lot of people died and a lot more are going to die unless he gets a lot smarter, a lot quicker," Mr Biden said.

Mr Trump objected to Mr Biden using the word "smart."

"You graduated either the lowest or almost the lowest in your class," the president said. "Don't ever use the word smart with me. Don't ever use that word."

Local rules required everyone in the room to wear masks, but of the president's family members present only US First Lady Melania Trump donned a face covering during the debate.

Due to the pandemic, the forum at Case Western Reserve University had a small, socially distanced audience and the traditional opening handshake was skipped.

Who won the debate?

In a debate that was the political equivalent of a food fight, the winner is the man who emerged least covered in slop.

On Tuesday night, that man was Joe Biden - if only because his main goal was to prove to Americans that he could hold up under pressure, that he had not lost a step due to his advancing age. He had to show he could take a pie to the face, metaphorically speaking, and keep his cool.

He mostly met that standard, although it was at least in part because Donald Trump, by his constant hectoring and interruptions, seldom gave the former vice-president a chance to say something truly damaging to his own cause.

Twitter Trump - the unconventional, bombastic, insulting and rumour-mongering aspect of this president - was on full display throughout the hour and a half event. Unfortunately for the president, many Americans, even his own supporters, find his social media persona one of his more unattractive attributes.

Trump needed this debate to shake up a race that is tilting against him - and has been remarkably stable, through economic, health and social adversity.

Nothing about this hour-and-a-half free-for-all seems likely to alter the dynamics of this contest or change the minds of the one in 10 American voters who say they are still undecided (although perhaps they'll resolve never to watch another one of these).

Anything resembling a substantive exchange was buried in a cavalcade of bloviation and bickering - and because of this, it was a missed opportunity for the president.

How did their families come into the debate?

Mr Biden referred to claims by anonymous sources that Mr Trump had once called members of the military "losers", a report denied by the president and a number of his former and current aides.

The Democrat spoke of his late son, Beau, who served in Iraq. "He was not a loser, he was a patriot!" said Mr Biden angrily.

Mr Trump brought up the Democrat's other son: "Really? Are you talking about Hunter?"

"I'm talking about my son, Beau Biden!" said Mr Biden.

"I don't know Beau," said Mr Trump. "I know Hunter. Hunter got thrown out of the military. He was thrown out, dishonourably discharged for cocaine use. And he didn't have a job until you became vice-president."

Shouting over Mr Trump, Mr Biden said: "My son, like a lot of people, like a lot of people you know at home, had a drug problem."