I would show an ad telling the sad tale of his first wife. Remind the American people that he has absolutely no "family values" (not something I care about of course, but it's clearly a buzzword the American public likes). Ask if a man who couldn't even care about his crippled wife can even care about the American people. The obvious truth is that he doesn't give a damn--he cares about McCain and McCain only. A truly despicable human being.
Good Lord. Do you really think that implying Obama is nothing more than a vapid celebrity equates with a personal attack like this? But then again I must remember, in Obama world, questioning the Messiah warrants the death penalty. Listen, maybe you can't tell the difference, but the average American voter knows the difference between comparing policy positions and a personal attack.
Seriously, though. You don't want to go down that route. Especially given the circumstances of the divorce, and the fact that John McCain's ex-wife "loves him to death" and has campaigned for him enthusiastically. She could appear in an ad, refute it, and decry Obama's false political attacks. Bam. Obama campaign over.
Corzine's hapless opponent in 2005 (can't remember his name) tried something like this. Corzine's ex-wife actually appeared in the ad. "He let his family down, and he'll let New Jersey down." Voter backlash enabled Corzine to win in a walk.
But if you want to try this, go ahead. I would imagine that being shut out for eight years has made you bunch more cautious, but I guess not.