John McCain, 2000:

“I just have to rely on the good judgment of the voters not to buy into these negative attack ads. Sooner or later, people are going to figure out if all you run is negative attack ads you don’t have much of a vision for the future or you’re not ready to articulate it.”

As the article notes, 100% of McCain’s ads have been negative (I haven’t seen a positive ad from McCain here in PA since before the conventions).