Biden has a chance to make history with his choice of a deputy. He has said he will pick a woman and has African American contenders on his shortlist. A black, female running mate would be a first and a plus for diverse representation.
Hillary Clinton is the only woman to have been a major party presidential nominee in the US. Geraldine Ferraro and Sarah Palin were on losing tickets.
The vice-presidential pick is a balancing act. The deputy is less useful in helping the main candidate win than potentially helping that person to govern. Al Gore, Dick Cheney and Biden were influential vice-presidents.
The pick can have a positive impact on the race if they reassure voters by being clearly qualified and offer something the nominee lacks. Biden, Cheney and current Vice-President Mike Pence were meant to bolster less-experienced bosses.
But Clinton's selection of Tim Kaine was more of a complacent choice for governing than winning when she needed a jolt of excitement to counter the limelight-hogging Trump. And John McCain's choice of Palin to get a poll boost only called his own judgement into question.
There is a political side to the role that is above what is required of most cabinet appointees. The VP ideally should have some extra wattage, as they often run for president themselves.
Despite being ahead in the polls and doing better than Clinton with white voters, Biden's standing with black voters is only average for a Democrat. Any complacency about turnout could be lethal with greater voting challenges expected with the pandemic.
Biden would be 78 at inauguration and may only serve one term, so the first requirement is to pick someone qualified and comfortable enough with the role.
Essentially, that divides the candidates mentioned into real contenders and longer shots. At the top of the known list would be former presidential candidates Senator Kamala Harris and Senator Elizabeth Warren, and former National Security Adviser Susan Rice. They are all highly experienced and Biden knows them better than other options.
It has been a very messy process so far, resembling a primary contest with different factions publicly lobbying for different candidates. It could be a preview of party infighting for influence should Biden win.
Harris was accused by Biden hangers-on of being too ambitious and insufficiently loyal. A late push for Congresswoman Karen Bass may have stalled over old links to Cuba and a video of her praising Scientology in 2010. But Bass also appears to be popular with Democratic officials. Another contender is Senator Tammy Duckworth, a military veteran.
The ongoing pandemic and protests against policing may have reduced the chances of several governors, Mayor Keisha Lance Bottoms and Congresswoman Val Demings, a former police chief.
Biden's choice is particularly interesting given the circumstances in which he would find himself should he win.
He would have multiple crises to confront, including the pandemic; economy; racial justice and inequality; climate change; the US health system; repairing America's alliances; dealing with China, Iran and North Korea; voting reforms; the fallout from the Trump Administration's pushing of governing norms and customs, and potentially Supreme Court positions to fill.
That would require an entire cabinet of VP-quality officials.
