US President Donald Trump and his White House challenger Joe Biden have fiercely clashed in the opening moments of their first live TV debate.
Mr Trump, a Republican, accused his rival of being beholden to socialists in his party, saying: “They’re going to dominate you, Joe, you know that.”
“I’m the Democratic party now,” retorted Mr Biden, a Democrat.
The 90-minute primetime duel in Cleveland, Ohio, is the first of three between the two rivals.
Opinion polls indicate Mr Biden has a steady single-digit lead over Mr Trump with 35 days until election day.
As the two candidates tussled over healthcare on Tuesday night, Mr Biden said: “Here’s the deal: everything he’s saying so far is simply a lie.
“I’m not here to call out his lies. Everybody knows a liar.”
Mr Trump hit back: “Joe, you’re the liar.”
Mr Trump challenged his rival to say whether he would pack the Supreme Court, adding more justices to tilt its ideological balance, as some Democrats have urged.
The president also demanded Mr Biden release a list of his nominees for the Supreme Court.
But Mr Biden would not be drawn.
“Will you shut up, man?” the Democrat said.
“Who’s on your list, Joe?” Mr Trump said. “He’s going to pack the court.”
The moderator, Chris Wallace, cut in to move the debate on.
“That was really a productive segment,” said Mr Biden with apparent sarcasm. “Keep yapping, man.”
Mr Trump replied: “The people understand, Joe. Forty-seven years, you’ve done nothing.”
The president later questioned why a company co-founded by his challenger’s son, Hunter Biden, had received $3.5m from a Moscow billionaire, according to a report released by Senate Republicans.
Mr Biden denied the claim, and the two shouted over one another.
As the moderator tried to cut in, the Democrat said: “It’s hard to get any word in with this clown, excuse me, this person.”
“Here’s the deal. We want to talk about families and ethics, I don’t want to do that, I mean, his family we could talk about all night.”
As the debate turned to law and order, Mr Trump said that Mr 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, Mr Biden warned of “predators on our streets” who were “beyond the pale”.
Mr Trump said: “You can’t even say the word ‘law enforcement’ because if you did say those words you would lose all of your radical left supporters.”
The president challenged Mr Biden to say whether he was in favour of law and order.
“Law and order with justice where people get treated fairly,” Mr Biden said.
In response to a question from the moderator, Mr Biden also said: “I’m totally opposed to defunding the police officers.”
Mr Trump was asked by the moderator if he was prepared to condemn white supremacists and militia groups.
“Sure,” the president said. “I’m willing to do that.”
“Then do it, sir,” said the moderator.
After a moment’s pause, Mr Trump said: “You want to call them, what do you want to call them? Give me a name, who do you want me to condemn?”
Pressed again to condemn white supremacists, Mr Trump said: “Stand back and stand by, but I’ll tell you what, somebody’s got to do something about antifa and the left.”
In a particularly feisty clash, 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 angrily said his late son, Beau, who served in Iraq and was awarded the Bronze Star, was not a loser.
“He was not a loser, he was a patriot!” said Mr Biden.
Mr Trump cut in: “Really? Are you talking about Hunter?”
“I’m talking about my son, Beau Biden,” said the Democrat.
“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.
“And once you became vice-president he made a fortune in Ukraine, in China, in Moscow and various other places. He made a fortune and he didn’t have a job.”
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.
“He’s overtaken it. He’s fixed it. He’s worked on it. And I’m proud of him.”