His campaign has not set a date for the announcement and there is still time for the contenders and their advocates to make appeals to Mr Biden, who is 77 and would be the oldest person elected president if he wins the race to the Oval Office.
Mr Biden, who himself served as vice president to Barack Obama, had initially indicated in May he would make a decision around August 1 but campaign sources now suggest a decision could come in the week starting on August 10.
That is one week before the party convention formalises Mr Biden’s nomination to challenge President Donald Trump for the keys to the White House.
Running mates are often announced on the eve of a convention.
As he prepares to make his choice, a committee established to vet the contenders has provided Mr Biden with briefing materials.
Mr Biden will likely soon begin one-on-one conversations with those under consideration, which could be the most consequential part of the process for a presidential candidate who values personal connections.
He is also facing calls to choose the first black woman to compete on a major party’s presidential ticket.
The leading contenders include California Senator Kamala Harris, California Representative Karen Bass and Obama national security adviser Susan Rice.
The deliberations remain fluid, however, and the campaign has reviewed nearly a dozen possible running mates, although Mr Biden has made it clear he will choose a woman.
“For Joe Biden, this is crunch time – after all the vetting, all the investigations into the prospective nominees, it’s now up to Joe. It’s personal,” said former New Mexico governor Bill Richardson, who was vetted for vice president in 2008.
“It’s now about his gut feeling.”
The selection amounts to the most significant choice Mr Biden has confronted in his nearly five-decade political career.
As a decision looms, the camps are jockeying for position.
We’re facing some of the biggest challenges in our history — and it’s abundantly clear Donald Trump just isn’t up for the job.
We need real leadership — and we need it now.— Joe Biden (@JoeBiden) July 31, 2020
Ms Harris’ allies mobilised this week after Politico reported that the co-chair of the vetting committee, former Connecticut senator Chris Dodd, was concerned about her tough debate-stage performance and that she has not expressed regret.
Several California elected officials and labour leaders initiated a call with the vetting team to emphasise that Ms Harris has strong support among labour and political leaders in her home state.
The call was organised by Lieutenant Governor Eleni Kounalakis who said: “A group of us really felt we needed to organise and speak out and correct the record because she has tremendous support.”
Beyond emphasising their strong relationships with Ms Harris, they also pushed back against the idea that Ms Harris would not be a loyal partner.
Millions of people across our nation are teetering on a cliff right now. Rent is due tomorrow. Bills need to be paid.
We have the answers already but reckless Republicans won't act: recurring $2k payments, expanded unemployment insurance, and nutrition assistance.— Kamala Harris (@KamalaHarris) July 31, 2020
Ms Harris, while not directly addressing her vice presidential prospects, told a group of young black women that it is common for black women to face resistance when they exercise their power.
“There will be a resistance to your ambition. There will be people who say to you: ‘You are out of your lane,’” she said during the digital summit.
“They are burdened by only having the capacity to see what has always been instead of what can be… I’ve had that experience my entire career.”
Mr Biden has sought feedback on his pick from Mr Obama, who has provided advice but has insisted the choice is Mr Biden’s to make.
Biden allies say his wife, Jill, and sister, Valerie Biden Owens, are likely to play a key role in the decision, as they have with many of his biggest political decisions throughout his career.
Jill Biden has held online campaign events and fundraisers with virtually all the potential contenders in recent weeks, as has Mr Biden himself.
On Thursday night, Ms Bass joined Mr Biden for a virtual fundraiser that raked in 2.2 million US dollars.
On Friday night, Mr Biden held a virtual fundraiser with Elizabeth Warren, who has also been considered as a running mate.
Mr Biden said the event raised more than 1.7 million US dollars from over 50,000 grassroots donors.
“We’ve known each other a long time. Her fearless work for a just America has transformed lives and inspired millions, including me,” Mr Biden said of the Massachusetts senator.
Ms Warren said: “This is a time of unprecedented crisis.”
“But I wake up every single day with a heart full of hope and here is why: Vice President Biden is meeting the moment.”
