It's all beautifully summed up here by Kelly McParland:
Barack Obama can’t possibly be bright enough to capture the Democratic presidential nomination and dumb enough to immediately undermine it by offering second spot on the ticket to Hillary Clinton.
Hat-tip to Justin Webb, who puts it nicely:
...it's not just the perceived gracelessness of her demeanour in recent hours: it's the simple fact that Barack Obama does not want That Man down the corridor. He wants Bill for his ambassador to Vanuatu. It's the Bill, stupid.