Who might replace Biden as Democrat’s presidential nominee?

Vice-President Kamala Harris, who is already on the ticket, is an obvious choice to replace Mr Biden.

As vice-president, she has become the face of the administration’s campaign to protect reproductive rights after the Supreme Court’s overturned Roe v Wade.

Ms Harris has proved to be a loyal ally to the president and fiercely defended his debate performance. After the event, she admitted the president had a “slow start” but argued he went on to provide more substantive answers than Trump.

“People can debate on style points, but ultimately this election and who is the president of the United States has to be about substance,” Harris told CNN Thursday night.

Ms Harris has the strong name recognition that comes from the job of vice president, but she has struggled with low approval ratings throughout her tenure.

Forty-nine percent of Americans disapprove of Ms Harris, while 39% approve, according to polling averages tracked by FiveThirtyEight.

Ms will also have a prime-time moment that could vault her ahead of the pack of potential presidential contenders when she faces off against Trump’s pick for vice-president. The BBC’s US media partner CBS is scheduled to host a vice presidential debate before the Democratic National Convention in August.