Some numbers: America has had a total of 48 vice presidents. Of those, 14 became president, either through election or succession. Of those 14, only two were vice presidents to presidents who had gone on to be elected president. (Those were President Jefferson (served under President John Adams, who had been vice president under President Washington) and President Ford (served under President Nixon, who had been vice president under President Eisenhower).)
The ability to continue on in the stead of a president is absolutely the most essential role and duty of the vice president, and that should be the primary factor in choosing a partner for the 2020 ticket: someone that can take over. That’s more true as there are indications that Biden would not seek a second term if elected, which would put more weight on this pick being an exception to that rule.
One of Biden’s benefits, having been vice president, is that he knows the job. He knows the Senate, and he knows the ceremony. He’s been steeped in the day-to-day politics without being in a particularly accountable or involved position. He’s had the confidence of the president, ridden in the front passenger seat while the president drove, ready to steer if he fell out.
After readiness to lead, the pick does several things for a campaign. The all-important fundraising, for one. Most politicians have a set of go-to donors, some of whom will already have communicated how much more they could give, should their favorite daughter be tapped.
Then there’s support in states, regions, or with particular groups the candidate needs to carry. This depends on the race, but is usually at least a partial factor in every choice for vice president, even if it’s not the main one. An offshoot of this, for current officeholders, is what will become of their old job. If they’re a senator, will their seat be safe?
Surrogacy is also a big part of the pick. Can they campaign well? Draw a crowd? Can they gain access to venues the main candidate either doesn’t want to, or wouldn’t be as well received in? Do they have any rhetorical specialties? Second languages?
Biden will announce his choice sometime this week. It should be interesting to see the rollout, given the otherwise odd nature of this election so far.