The former vice president has publicly pledged that his VP pick will be a woman, and the US has never had a female vice president. But that still leaves a lot of potential nominees. Here's a look at a shortlist of frequently mentioned potential candidates.
Kamala Harris & Stacey Abrams
Biden became the Democratic front-runner largely because of the overwhelming support he's received from African-American voters. He has said his administration would reflect the country's demographics, leading many to believe he is considering minority or black politicians like Kamala Harris or Stacey Abrams.
Harris, 55, a senator from California, would balance a ticket led by a 77-year-old white man. As the daughter of Jamaican and Indian immigrants, she could help rally black voters, a crucial Democratic voting bloc.
Abrams, the former minority leader of the Georgia House of Representatives and a close runner-up in the 2018 state gubernatorial election, is regarded as a rising star in the party. And at 46, she would create important generational balance on the ticket that might even help Biden draw in younger Democratic voters, many of whom have supported Sanders. But Abrams, with little experience on the national stage, is likely to face concerns over not being qualified to step up if Biden became unable to carry out his duties as commander in chief.
Amy Klobuchar & Elizabeth Warren.
As Biden is already popular among minorities, it's possible he will instead focus on November when making his choice.
Amy Klobuchar, a senator from Minnesota, who as a presidential candidate frequently pitched her crossover appeal with GOP voters, could help Biden build his own electability message with Republicans who are unhappy with Trump. She also might boost Biden's prospects in Michigan, Wisconsin and Pennsylvania, which, like Klobuchar's home state, are crucial Upper Midwest battlegrounds.
Klobuchar's decision to drop out and endorse Biden ahead of Super Tuesday was credited with helping him quickly consolidate the moderate factions of the Democratic Party and cruise to a series of victories. But some analysts say she wouldn't bring a lot of balance to the ticket. Klobuchar is white and moderate -- too much of the same things Biden offers.
How about the leftist senator from Massachusetts, Elizabeth Warren? Selecting Warren would be something of an olive branch to the more liberal parts of the democratic party, which could help Biden increase his turnout in November. That may be a major factor in Biden’s thinking, given President Trump's popularity among Republicans and the likelihood of a long, tough campaign ahead.
Warren wouldn't face any questions about her readiness to take over for Biden. But Biden has pitched himself as a bridge to a new generation of Democratic candidates. And at 70, she might not be in the right position to be the future face of a post-Biden party.
Biden Versus Trump in the general election
Biden has led Trump in head-to-head polls consistently and sometimes quite significantly, but so did Hillary Clinton. Adding to the uncertainty is the fact that the battleground states in this election may not be the ones we traditionally expect. States like Michigan, Georgia, and maybe even Texas are becoming harder to predict, whereas states like Ohio or Florida are less so. We cannot take our eyes off these states until the very end.