Vice president Kamala Harris has moved swiftly to lock up Democratic delegates behind her campaign for the White House after President Joe Biden stepped aside amid concerns he would be unable to defeat Republican Donald Trump.

Mr Biden’s exit on Sunday, prompted by Democratic worries over his fitness for office, was a seismic shift to the presidential contest that upended both major political parties’ carefully honed plans for the 2024 race.

Aiming to put weeks of intra-party drama over Mr Biden’s candidacy behind them, prominent Democratic elected officials, party leaders and political organisations quickly lined up behind Ms Harris in the hours after Mr Biden announced he was dropping his re-election campaign.

Mr Biden’s departure frees his delegates to vote for whomever they choose. Ms Harris, whom Mr Biden backed after ending his candidacy, is thus far the only declared candidate and was working to quickly secure endorsements from a majority of delegates.

Later on Monday, Mr Biden called into a campaign staff meeting and promised he will be “out on the road” in support of Ms Harris.

He said the ‘mission hasn’t changed’ with Ms Harris poised to lead the party.

Ms Harris acknowledged the Democratic ‘rollercoaster’ after Mr Biden’s exit from the 2024 race, and said she will unite party and nation.

Additional endorsements on Monday, including Maryland Governors Wes Moore, Gretchen Whitmer, JB Pritzker and Andy Beshear, left a dwindling list of potential rivals to Ms Harris.

Speaker emerita Nancy Pelosi, who had been one of the notable holdouts to Ms Harris, initially encouraging a primary to strengthen the eventual nominee, endorsed the vice president on Monday.

Ms Pelosi said she was lending her “enthusiastic support” to Ms Harris’ effort to lead the party.

More than 700 pledged delegates have told AP or announced that they plan to support Ms Harris at the convention, which is over one-third of the pledged delegates she needs in order to clinch the nomination.

Democratic National Committee rules most recently set 1,976 pledged delegates as the benchmark to win the nomination.

Winning the nomination is only the first item on a staggering political to-do list for her after Mr Biden’s decision to exit the race, which she learned about on a Sunday morning call with the president.

If she is successful at locking up the nomination, she must also pick a running mate and pivot a massive political operation to boost her candidacy instead of Mr Biden’s with just over 100 days until Election Day.

On Sunday afternoon, Mr Biden’s campaign formally changed its name to Harris for President, reflecting that she is inheriting his political operation of more than 1,000 staffers and a war chest that stood at nearly 96 million dollars at the end of June.

It got bigger by Monday morning: Campaign spokesperson Lauren Hitt said Harris had raised 49.6 million dollars in donations in the first 15 hours after Biden’s endorsement.

Ms Harris spent much of Sunday surrounded by family and staff, making more than 100 calls to Democratic officials to line up their support for her candidacy, according to a person familiar with the matter who spoke on the condition of anonymity to discuss the effort.

It comes as she tries to move her party past the painful, public wrangling that had defined the weeks since the Mr Biden’s disastrous June 27 debate with Mr Trump.

Speaking to party leaders, Ms Harris expressed gratitude for Mr Biden’s endorsement but insisted she was looking to earn the nomination in her own right, the person said.