President Donald Trump and Democratic challenger Joe Biden began the first presidential debate with heated exchanges over coronavirus and health care.
The two men frequently interrupted each other with angry interjections, with Mr Biden eventually snapping at his opponent: "Will you shut up, man?"
As the discussion about the Supreme Court quickly turned to coronavirus, Mr Trump claimed, without evidence, two million people would have died if his opponent were president.
Moderator Chris Wallace of Fox News pleaded with Mr Trump, stating that COVID-19 would be discussed later in the debate.
He then asked Mr Trump about whether he had a plan to replace the Affordable Care Act, and the president said: "First of all, I guess I'm debating you, not him, but that's OK. I'm not surprised."
Mr Biden laughed at his opponent's jabs, but also appeared to get upset at times.
"Here's the deal, the fact is that everything he's saying so far is simply a lie," Mr Biden said. "I'm not here to call out his lies. Everybody knows he's a liar."