Those were very different times though, and I doubt anybody wants to draw comparisons with Calhoun, who may rank as one of the worst VPs.

I really don't know. Typically the vice-presidency is a means of balancing or filling out the geographic and philosophical appeal of the ticket, perhaps smoothing out hard-feelings once the ticket is set.

Until some convention delegates get earned via elections and caucuses this seems premature.

someone below Social Security eligibility age in the mix somewhere.

I'm not really speculating on a VP at this point; that will depend on who gets the nomination. Biden really isn't on my short list of people I'd like to see in that position, though.