According to ABC News, this was the attack ad on Barack Obama and Jeremiah Wright that John McCain refused to let run near the end of the election season.
I don't think it would have made a difference in the outcome if he'd run it--the Wright issue was long over by then, and the other deficits McCain had to make up were too great--but I'm sure the pressure was high on McCain to do so, and I'm glad he didn't. And there's no question that Sarah Palin would have run it in a heartbeat.