[x]

This reminds me of those puzzles we had when we were kids:

There is only one combination and not many ways of getting there. I think it's Biden-Harris. I'm not saying it's a good ticket or a winning ticket or the best ticket. I'm saying it's the one that checks all the boxes.

If Biden loses, it's going to be hard to get a plausible ticket. Warren-Booker? Warren-Harris? Warren-Bernie? Bernie-Warren? Bernie-Booker? Bernie-Harris? All probably weaker than a ticket with Biden and somebody who checks the two boxes.

I'm pretty sure Beto or Buttigieg won't be nominated for either office whatever happens.

[Verginius Rufus]

I don't know who the Democrats will wind up nominating--at the moment I would guess that Warren has the best chance but she could prove to be another flash in the pan like Beto.

There is no rule that the VP nominee has to be someone who ran for President--it could be a governor or senator who isn't in the presidential race.