I really really doubt she would pick Warner, and I also doubt he'll ever get involved in a national campaign if he hasn't already
I wouldn't support him for President (in the primaries), but there are numerous benefits to him being the eventual nominee's running mate. He underlines experience, he's popular in a swing state, he's wouldn't steal attention from the top of the ticket, and he's not young so he wouldn't cause problems in the administration if they were to win.
Julian Castro would be an easy answer for Clinton.
Wow, good answer. I think it makes sense.
Castro needs to win statewide first. He probably won't be ready in time for '16, but maybe '20 or '24.