Even based on approval rating, Bush is not even the worst. There are a few that were worse than Bush, in that respect.

I believe that if Bush didn't go to war with Iraq, it's quite possible he could have wound up being one of the best. He had a 90% approval rating right after 9/11. One of the main reasons his approval dropped so much was because of the invasion of Iraq (if I remember correctly, Afghanistan was 'approved' by most citizens to find Bin Laden).