Who could challenge Harris for Democratic nomination?

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 is not a done deal, however.

Several others have been touted as potential replacements in the weeks leading to Mr Biden's withdrawal.

Many have paid tribute to Mr Biden after his announcement - but crucially almost none have said explicitly that they support the Harris endorsement.

Delegates will vote next month at the Democratic National Convention to officially confirm who will replace Mr Biden.

Here is a look at the names who could challenge Ms Harris.

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 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 political control 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."

That, however, was not an endorsement of Ms Harris.

California's governor is one of the Biden administration's fiercest surrogates. But he has political ambitions of his own.

He is often listed as a possible 2028 candidate, but many Democratic pundits now say that he could 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 was announced. But his statement on Twitter was brief, and mentioned nothing of his own intentions nor commented on the endorsement of Ms Harris.

It is no secret that Transportation Secretary Pete Buttigieg has presidential aspirations.

He ran for president 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 did not comment on his endorsement of Ms Harris.

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" after the president announced his withdrawal from the election race but - like most names touted to replace him - said nothing of what comes next.

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 did not immediately comment on Mr Biden's decision to withdraw from the election race.

The list of potential nominees stretches beyond these Democrats, as the party has developed a deep bench of possible future presidential candidates.

Kentucky Governor Andy Beshear, a two-term Democratic governor in a very conservative state, has earned growing national attention since his 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, also has been mentioned as a potential replacement for Mr Biden.

A Reuters IPSOS poll released Tuesday found the only person who could beat Trump in November was Michelle Obama. But the former first lady has repeatedly said she does not have presidential aspirations.