If the Clintons think obama, is going to blame them for his loss, they will destroy him before the election (to clear their name) but only if they think he is going to loose.
If they think he is going to win they may wait until after the election, but only destroy obama if he starts blaming them for anything (they go to great lengths to protect each other), they would have no compulsion in bringing down the presidency (it would not surprise me if she tells obama straight out, I will destroy you if you do not replace Biden with me, the she does anyway).