It should be a question for the big 3 anyway. Warren, Biden, and Bernie are all septuagenarians. I think it would be very appropriate to demand some candor when it comes to "estate planning", so to speak, if they were to be the candidate/POTUS.
The VP is often a throwaway position, but in this case, the choice could very easily end up serving as POTUS. This should be addressed.
This really isn't a partisan issue. Trump is, by all estimation, an obese, unhealthy 73 year old man.
I love Bernie, but it is really damning that all of the serious candidates are so old. The D's need fresh blood desperately.