Andrew Sullivan: It is for many in the Obama camp an unthinkable thought. But politics is sometimes the art of adjusting today to what seemed inconceivable yesterday. I'm talking about the possibility -- and the powerful logic -- of a unity Obama-Clinton ticket for the Democrats. I hesitate to propose this, but I do think it is now worth actively considering for the first time in this campaign. The test of a president is his ability to recognise his own weaknesses and adjust to them. If he can do that while strengthening his core message, and make his own election close to unstoppable, what would hold him back?
