Please!
Anyone spending that amount of money on an ad would have cleared it with McCain first. Second, there are all manner of focus groups which help them keep the ads on target.
The McCain folks would have known about it in detail from the beginning. If they didn't they should have. "Plausible deniability" isn't possible at this part of a campaign for the President of the United States.
So McCain and/or his ilk came up with an ad which reflected badly upon McCain and his ilk. So he cancelled it.
What a way to be a "hero". In reality it's sleezy from start to finish.
Arf