Barack and Michelle Obama endorse Kamala Harris for president

Backing of former US president is expected to boost Ms Harris's election campaign against Donald Trump

Kamala Harris speaks on the phone with Barack and Michelle Obama, who have endorsed her as the Democrats' presidential candidate. Reuters

Barack and Michelle Obama have endorsed US Vice President Kamala Harris in her bid for the White House.

The backing of two of the most popular Democrats adds yet more fuel to Ms Harris's powerful momentum towards officially clinching the nomination to run against Republican Donald Trump in November.

“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,” Mr Obama, who served as president from 2009-2017, told Ms Harris in a phone call she posted online.

Ms Obama said: “I can’t have this phone call without saying to my girl, Kamala, I am proud of you.

“This is going to be historic,” she added.

Ms Harris, who has known the Obamas since before his election in 2008, thanked them for their friendship and said she looks forward to “getting there, being on the road” with them in the three-month campaign blitz before Election Day on November 5.

“We’re gonna have some fun with this too, aren’t we?” Ms Harris said in the call.

The Obamas are perhaps the last major Democratic Party figures to endorse Ms Harris formally, a reflection of the former president’s desire to remain, at least publicly, a party elder operating above the fray.

The Obamas remain prodigious fundraisers and popular surrogates at large campaign events for Democratic candidates.

Ms Harris, 59, jumped into the election after weeks of turmoil over 81-year-old Biden, who stepped aside after a dismal debate performance against Mr Trump accelerated concerns over his mental capacity and persistently low polling numbers.

She has since launched a blistering attack on Mr Trump and his “extremist” Republicans.