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.
Biden called the president a "clown" and told him to "shut up". Trump brought up drug use by his rival's son.
Opinion polls suggest Biden has a steady single-digit lead over 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.
How did the two clash on race and white supremacy?
In one of the most talked about exchanges of the night, the president was asked by the moderator 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.
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."
Earlier, Biden said: "This is a president who has used everything as a dog whistle to try to generate racist hatred, racist division."
Trump countered that Biden, while supporting the 1994 crime bill, had referred to African Americans as "super predators".
The Democrat denied saying such a thing. In 1993, while chairman of the Senate Judiciary Committee, Biden warned of "predators on our streets" who were "beyond the pale".
What did they say about coronavirus?
Biden said 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," Biden said.
Trump objected to 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.
What other insults were exchanged?
In the vitriolic back and forth, Biden, 77, told Trump, 74: "You're the worst president America has ever had."
The former vice-president under Barack Obama also said of Trump: "Everybody knows he's a liar."
Trump defended his effort to swiftly fill a US Supreme Court seat to cement a 6-3 conservative majority on the bench.
As the president demanded Biden release a list of his own judicial nominees, Biden snapped: "Will you shut up, man?"
At another point, Biden said: "It's hard to get any word in with this clown. Excuse me, this person."
He also called the president "Putin's puppy" in a reference to Russia's president.
Why is the moderator being criticised?
It was Wallace's second time moderating a presidential debate and he at times struggled to rein in the quarrelling rivals.
At one point he urged the president to stop his interruptions.
The Fox News host said: "I think that the country would be better served if we allowed both people to speak with fewer interruptions. I'm appealing to you, sir, to do that."
Trump replied: "Well, and him, too."
BDST: 1225 HRS, SEP 30, 2020