George Packer in The Atlantic:

Rumsfeld was the worst secretary of defense in American history. Being newly dead shouldn’t spare him this distinction. He was worse than the closest contender, Robert McNamara, and that is not a competition to judge lightly. McNamara’s folly was that of a whole generation of Cold Warriors who believed that Indochina was a vital front in the struggle against communism. His growing realization that the Vietnam War was an unwinnable waste made him more insightful than some of his peers; his decision to keep this realization from the American public made him an unforgivable coward. But Rumsfeld was the chief advocate of every disaster in the years after September 11. 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.