If Clinton is demanding the VP slot and will not support him without it, it is she who is dividing the party. Obama has the right, and the OBLIGATION TO HIS VOTERS, to choose a VP that he is comfortable with and that he believes will do the best possible job with him. Period. If he is coerced in to a choice, he is breaking faith. If he chooses her of his own volition, fine. But if she refuses to fully back him and encourage support, that is HER fault.
I have no dog in this race, but it's just silly to blame someone for being divisive and not uniting the party because he doesn't cave to blackmail, if that should be the case.
Unless what you're suggesting is that people who support Hillary will not support the Democratic Candidate, the one she backs and supports. In which case, it seems lose-lose.
And, lesson in math for you: There is no such thing as a bigger half.