by Nicholas Beaudrot of Electoral Math
There has been an interesting discussion going on over at TPMCafe searching for the root causes of Bush's fall in popularity, which begain in mid-August '05, before hurricaine Katrina. On August 3rd, a bomb in Haditha killed 14 soldiers from an Ohio-based division, after 7 had died in the same area just two days earlier, again mostly from Ohio. I don't have a Lexis subscription, but I suspect if you look at the coverage this was the first time in a few months the press was jarred into covering Iraq in a negative way. Soon afterwards, Cindy Sheehan's campout started generating positive coverage for the anti-war movement. This, I think, was the beginning of the end of net positive approval ratings for Bush.
Update: some antecedent clarity here. The Haditha bombings were the real start of Bush's decline; Sheehan managed to push the rock down the hill a good deal.