The debate is broadcast on the Washington Post website.
At the start of the debate, Trump and Biden got into an argument over the U.S. health insurance system.
In particular, the current US president said that Biden intends to "transform the health care system into socialism."
"The thing is, everything he said before was just a lie ... Everyone knows he's a liar," Biden said.
Also, the US presidential candidates discussed the situation with the coronavirus.
Biden said Trump has no plan to fight COVID-19.
In turn, Trump said that a coronavirus vaccine will soon be created in the United States.
In addition, they discussed the candidacy of a new judge of the US Supreme Court.
Biden said a new judge should be appointed after the end of the election.
In turn, Trump said that Republicans won the previous election and have the right to choose a judge.
The first debate between Trump and Biden ahead of the US presidential election takes place in Cleveland.