• Several others were touted as potential replacements for Mr Biden but have backed Ms Harris.
• If the endorsement becomes official, a running mate will be needed.
Image: Screengrab
US President Joe Biden on Sunday announced he would end his re-election campaign, and said Kamala Harris, his vice-president, should take his place.
"I want to offer my full support and endorsement for Kamala to be the nominee of our party this year," he wrote on X. "Democrats — it's time to come together and beat Trump."
Ms Harris taking over looks likely, although it is not a done deal.
Several others were touted as potential replacements for Mr Biden but have backed Ms Harris. If the endorsement becomes official, a running mate will be needed.
Delegates will vote next month at the Democratic National Convention to officially confirm who will replace Mr Biden, and the candidate for vice-president.
The following names could be in the mix.
Michigan Governor Gretchen Whitmer
Gretchen Whitmer, the two-term governor of Michigan, is an increasingly popular Midwest Democrat who many pundits speculate will run for president in 2028.
She has campaigned for Mr Biden in the past and has not been shy about her political aspirations.
She told The New York Times that she wants to see a Generation X president in 2028, but stopped short of suggesting that she might fill that role.
In 2022, she led a campaign that left Michigan Democrats in control of the state's legislature and the governor's mansion.
That allowed her to enact a number of progressive policies, including protecting Michigan abortion access and the passage of gun safety measures.
Ms Whitmer quickly stated after Mr Biden's withdrawal that her job "will remain the same... doing everything I can to elect Democrats and stop Donald Trump".
California Governor Gavin Newsom
California's governor is one of the Biden administration's fiercest surrogates.
He is often listed as a possible 2028 candidate, but many Democratic pundits had suggested he could be in the race to replace Mr Biden.
Mr Newsom raised his national profile in recent years by being a key party messenger on conservative media, and via a debate against Florida Governor Ron DeSantis last year.
He stood by the president before his announcement. He travelled to Washington to attend meetings in July with Mr Biden and other top Democratic governors, and headlined a Biden campaign event in Michigan on the 4 July.
Mr Newsom again praised Mr Biden as a "selfless" president after his withdrawal, and said he backed the "fearless" and "tenacious" Ms Harris to face Trump.
Transportation Secretary Pete Buttigieg
It is no secret that Pete Buttigieg has presidential aspirations.
He ran in 2020 and is often touted as one of the Biden administration's best communicators.
Mr Buttigieg has managed a number of public crises during his time as transportation secretary.
He helped to oversee the government response to the East Palestine train derailment in Ohio, the Baltimore Bridge collapse and Southwest Airlines' scheduling crisis in 2022.
Mr Buttigieg stated on Twitter/X that Mr Biden had "earned his place among the best and most consequential presidents in American history".
He said he would do "all that I can to help elect Kamala Harris the next President".
Josh Shapiro, Pennsylvania Governor
Josh Shapiro has seen high approval ratings since he was elected in 2022 in a swing state Trump narrowly carried in 2016.
The governor, who previously served as the state's attorney general, has worked across party lines during his tenure.
He made national headlines last year after quickly rebuilding a collapsed bridge on a crucial Philadelphia highway - a major political victory for a first-term governor.
The speedy repair was hailed by many as the perfect infrastructure talking point for a potential 2028 presidential candidate.
Mr Shapiro said Mr Biden was one of the "most consequential presidents in modern history" and would "do everything I can to help elect Kamala Harris as the 47th President of the United States".
JB Pritzker, Illinois Governor
JB Pritzker, the governor of Illinois, has raised his profile in recent years by going after Trump and defending Mr Biden.
The billionaire businessman - heir to the Hyatt hotel chain - is quick to post criticism of Trump on social media.
After the debate he called Trump a "liar" and said he is a "34-count convicted felon who cares only about himself".
Like Ms Whitmer, Mr Pritzker has a track record of completing agenda items on progressive Democrats' to-do lists on issues like abortion rights and gun control.
He said Mr Biden had run "one of the most accomplished and effective presidencies of our lifetime". He has not commented on who should succeed him.
Other possible candidates?
The list of potential nominees to the ticket stretches beyond these Democrats, as the party has developed a deep bench of talent.
Kentucky Governor Andy Beshear, a two-term Democratic governor in a very conservative state, has earned national attention since re-election last year.
Maryland Governor Wes Moore found himself in the spotlight in recent months following the collapse of the Francis Scott Key Bridge in Baltimore.
Senators Amy Klobuchar and Cory Booker have run for president in the past and have some name recognition among Democrats.
Georgia Senator Raphael Warnock, who won a closely contested Senate race in a swing state.
And Arizona Senator Mark Kelly is another name under discussion. He is a former US Navy pilot and astronaut who won his senatorial seat in a key swing state.