The problem with Powell is the depth of his betrayal.
Though there were many that were deeply distrustful of the Bush administration, he was the one senior guy in it who was liked and trusted pretty much across the board. He was a natural for the top foreign policy guy, and as former Joint Chiefs chairman, everyone thought he’d have strong influence on Defense policy as well. He was the main proponent of the Powell doctrine, which emphasized military intervention only when the reason was compelling, there was strong international support, the military force to be used was overwhelming and there was a clear exit strategy. These were the touchstones of the initial Gulf War, and he was widely perceived as having been the father of the strategy that led to victory.
In contrast, the rest of the Bush administration didn’t have the level of public trust. Bush personally had virtually no foreign policy or defense experience. Everybody knew Rumsfeld and Wolfowitz were neoconservative hawks, and was pretty sure Cheney was one too. Rice was smart, but a touch out of her league.
Powell, everyone thought, was the pragamatist who would stand as a bulwark against the ideologues – the no nonsense military man who would protect the troops.
In the build up to the war, he was obviously uncomfortable with what was going on. Though the Rumsfeld/Wolfowitz camp was cheerleading for war (and Cheney was hiding in his bunker), Powell really needed to be convinced it was the right thing. He was, in many ways, the proxy for all of those who were unsure of the need for the war, the level of international support, the strategy and the exit plan (in short, the main tenets of the Powell doctrine). He was the guy who, due to his training, experience and personal integrety, would look at this in a clearheaded manner and give us all an objective read on what we should do.
Eventually, Powell came out for the war in a way that showed he was laying his credibilty on the line, domestically and internationally. All of a sudden, the one administration leader we all trusted to make the right military decision – to not commit troops unnecessarily – to not get us into another Vietnam – to stand up to the ideologues – had said that this war was the right thing to do. And by implication, he endorsed the Defense Department’s plans for doing it.
In the end, he was wrong. The reason why is really immaterial, because he put his considerable public trust behind the war without adequate basis. Everyone knew that Bush, Rumsfeld, Rice and the rest would shade and spin things in favor of the war. But when Powell, the guy we thought we could trust, was found to be doing the same thing, it was over for him.