There is a gentler way to call out McCain.  Obama could simply "feel sorry" for McCain.  "I feel sorry for John McCain.  It's sad really.  He has lost his moral compass and sacrificed his honor in his bid to be president.  He has aligned himself with the same people that savaged him in the 2000 primaries, he has embraced those that he previously derided, he has sold out his convictions, and reduced his campaign to little more than a set of ridiculous ad hominem attacks.  It's pathetic to see."  Essentially, a defensive posture is a losing posture.  As nearly everyone in the blogosphere seems to agree on this, it isn't clear why the Obama campaign "professionals" cannot see it.  Don't repeat the charges, but keep reminding people that McCain is actually making them.  Don't dignify them with a rebuttal, but use pity and mock scorn to dismiss them.  Roll your eyes and laugh it off as the ravings of a desperate old politician that can barely remember his own name.