I thought these sentences, written by George Packer in The Atlantic, pretty much said it all about Rumsfeld:

“Wherever the United States government contemplated a wrong turn, Rumsfeld was there first with his hard smile — squinting, mocking the cautious, shoving his country deeper into a hole. His fatal judgment was equaled only by his absolute self-assurance. He lacked the courage to doubt himself. He lacked the wisdom to change his mind.”