Maybe, just maybe, it’s now worth at least asking whether Hillary Clinton might wind up as the Democratic candidate for vice president. When the chatter about a Democratic “dream ticket” began last year, it was easy to dismiss. Either Clinton or Obama would win a clear victory in the primaries and, after what inevitably would be a contentious campaign, each would want as little to do with the other as possible. Clinton, if she emerged victorious, would instead choose some kind of national security graybeard to her political right, a retired general perhaps, or maybe even a Republican. Likewise, Obama...