Here are some quotes from the beginning of The Screwtape Letters by C.S. Lewis:

"The best way to drive out the devil, if he will not yield to texts of Scripture, is to jeer and flout him, for he cannot bear scorn."—Luther

"The devill . . the prowde spirite . . cannot endure to be mocked."—Thomas More

These quotes, taken from a different context, might provide a guide to how Obama should respond to negative attacks.  If Obama goes negative and nasty, he risks undermining his own message.  On the other hand, undermining the attacks by ridicule might defuse them better.  By doing so, he will not appear as nasty as he would otherwise.

Obama already has used ridicule effectively once.  In the very important tire pressure debate, Obama had a comment on McCain's flip-flopping, "We just agreed to a series of debates in the fall, but the most interesting one that's going on these days is the debate between John McCain and John McCain."

The material for riducule is there.  In response to the gravely serious charge of being called a celebrity, Obama could make fun of McCain appearing in Wedding Crashers.  And it does not have to be just for a counterpunch.  He can attack first with ridicule.  He can go after McCain's numerous flip flops with light humor, instead of dark threats of what a McCain Presidency would mean. 

There is an additional benefit by taking this route.  It should be apparent that McCain cannot take a joke.  He can call reporters "jerks," but if anyone insults him, watch out.  Ridicule might make McCain unhinged.  We just need one such moment caught on tape to seal the election.  Old Crankypants might be fun to the press when he is a bit grouchy, but all the fun is lost when he actually loses his temper.

It is not enough to just go negative.  You have to go negative with the right tone.  The American people appreciate humor, and they will respond better to it than to talk of impending doom.  Leave the talk of impending doom to the Republicans.