Former president Barack Obama told Kamala Harris he “couldn’t be prouder” as he endorsed her to replace Joe Biden as the Democratic candidate for the US election.
Mr Obama had so far remained quiet after other top Democrats gave the US vice president their backing in the days after Mr Biden pulled out of the race on Sunday.
He also released a statement after Mr Biden’s decision which suggested he was calling for an open contest to decide the Democratic nominee.
However, Ms Harris has now released a video which shows her speaking to Mr Obama and his wife, the former first lady Michelle, in a joint phone call in which they give her their support.
Mr Obama says: “We called to say, Michelle and I couldn’t be prouder to endorse you and do everything we can to get you through this election and into the Oval Office.”
Mrs Obama, speaking after a poll suggested she would win the US election if she chose to run, told the vice president in the call: “I can’t have this phone call without saying to my girl Kamala: I am proud of you. This is going to be historic.”
Ms Harris replies: “Oh my goodness. Michelle, Barack, this means so much to me.
“I am looking forward to doing this with the two of you – Doug [her husband] and I both. And getting out there, being on the road.
“But most of all, I just wanna tell you that the words you have spoken and the friendship that you have given over all these years mean more than I can express.
“So thank you both! It means so much. And… we’re gonna have some fun with this, too, aren’t we?”
Mr Obama then tells Ms Harris she is a “happy warrior”, before the former first lady adds: “And the country needs a happy warrior.”
Mrs Obama also told the probable Democratic nominee: “It’s time for us to rally around you, your candidacy. This is not on you, it’s not just on you and Doug, it’s on all of us… We’ve got to register, we’ve got to vote…. So, let’s all roll up our sleeves and make it happen.”
Ms Harris is almost certain to secure the Democratic nomination and would take on Republican candidate and former president Donald Trump in the race for the White House.
The Obamas have been slower to publicly endorse Ms Harris than other top Democrats.
Mr Biden, who served as vice president under Mr Obama between 2009 and 2017, immediately gave his vice president his support and urged the party to get behind her when he quit the race.
Endorsements quickly followed from Bill and Hillary Clinton and former House Speaker Nancy Pelosi.
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In contrast, Mr Obama released a statement after Mr Biden announced he was stepping down, saying: “I have extraordinary confidence that the leaders of our party will be able to create a process from which an outstanding nominee emerges.”
But his endorsement today comes after Sky News’ partner network NBC News reported that Mr Obama and Ms Harris have regularly been in touch since she announced her intention to run.
Governors Gavin Newsom and Josh Shapiro, once touted as potential substitutes for Mr Biden, are among dozens of Democratic elected officials who have shown their support for Ms Harris. Both could be in contention to be selected as her running mate and vice presidential candidate.
The Democratic party’s fundraising platform had its biggest day of the year after Mr Biden pulled out of the race, with nearly $50m (£38.7m) pouring in, with labour unions and advocacy groups also getting behind Ms Harris.