Bill Clinton is a narcissistic egotist.
He doesn't want to see a second President Clinton, certainly one who will be a more historic figure if just for the fact that she would be the first female President. He'll sabotage her once it appears she is a locked in frontrunner.
Either health reasons or a bimbo eruption will take Hillary down.
I'm not so sure.
Bill likes nothing better than being surrounded by adoring political naivete's. Hillary can pack them in.