I think the both Bushes began their decline with their failure to stop the murder of Terri Schiavo. Either one of them could have saved her, had innocent human life been more important to them than their own careers. And I think had either of them they shown the moral courage to do so, with the clear support of the other, Jeb would be the respected and beloved nominee and President.
Secondly, 100s of us FReepers carried a lot of water for Dubya during his administration. When he fired Rumsfeld after the 2006 mid-term, I dropped those buckets.