Who could replace Joe Biden and how are they chosen?

On Sunday, the incumbent said he would not run for a second term, with his party now scrambling to find a successor to take on Republican Donald Trump in November’s vote.

Here is how we got to this point and how the situation could unfold from here.

Mr Biden said that it was “in the best interest of my party and the country for me to stand down”.

He added that he would speak in more detail later this week to detail his decision. 

The president’s aides had previously said that only health would stop him from running in November – which could suggest that the diagnosis played a role. 

However, Mr Biden has been under pressure for some time. 

And while he has long been gaffe-prone, his performances have become increasingly erratic in recent weeks. 

This has reportedly led senior Democrats including Barack Obama and Nancy Pelosi to call on Mr Biden to step down. 

The Democratic National Committee chairman Jaime Harrison has said that there would be no automatic coronation for Mr Biden’s replacement. 

He added: “This process will be governed by established rules and procedures of the party. Our delegates are prepared to take seriously their responsibility in swiftly delivering a candidate to the American people.“

This is an unprecedented situation and the Democratic Party has not – as of Monday morning – offered many details on what happens next.

Any potential candidate will need to secure the nomination from the around 4,700 Democratic convention delegates.

This includes those pledged to Mr Biden, as well as the elected officials, former presidents, and other party elders known as superdelegates.

There has already been some confusion as to whether Kamala Harris, the current vice president, will automatically be pushed forward for the top job. While she is the obvious candidate, Democratic rules state only that delegates “in all good conscience” vote for the candidate they were elected to represent, with no mechanism for defectors. And some in the party have endorsed an open nominating process.

The person, who spoke on the condition of anonymity to discuss internal conversations, argued that Ms Harris would benefit from a competitive mini-primary ahead of the Democratic convention, because it would help her seal her bona fides as a strong candidate and diminish criticism that she’s been undemocratically anointed. 

That’s a charge the Trump campaign has already sought to use against her, and could loom large in the battle for undecided voters in battleground states.

The Democrats would want Ms Harris to be on the ballot having been given a vote of confidence but would not want a messy summer of competing candidacies.

The party will officially choose its presidential candidate at its convention on August 19 and will want as long as possible to be campaign their message. 

Minutes after announcing he was stepping back, Mr Biden offered his “full support” to Ms Harris, the party’s instant favourite for the nomination, to be the Democrat nominee.

Ms Harris in turn thanked Mr Biden for his “extraordinary leadership” and for making a “selfless and patriotic act” by stepping aside.

He said: “My very first decision as the party nominee in 2020 was to pick Kamala Harris as my Vice President. And it’s been the best decision I’ve made.

“Today I want to offer my full support and endorsement for Kamala to be the nominee of our party this year. Democrats — it’s time to come together and beat Trump. Let’s do this.”

Hollywood stars and donors have also backed her.

Ms Harris could potentially become the first woman president of the US and would be the obvious choice to encourage party continuity.

From here on in, all others on the list are possible and have not confirmed they will even try to run but are well positioned within the Democratic Party. 

California governor Mr Newsom is coming to the end of his second, and final, term in office and is said to be eyeing up the top job.

The Pennsylvania governor is a rising star but his time may come in 2028.

The California representative had been touted as another potential name in the frame.

But he will not run this time, he says, tweeting: “I am proud to endorse @KamalaHarris as our nominee. 

“Her trailblazing candidacy as the first African American woman and first Asian American will be a jolt of energy in our party. Our party can now run on a message of hope and a vision for the future.”