President George W. Bush is responsible for the ongoing misadventure in Iraq, and likely nothing could have stopped his administration from pursuing its long-standing plans against now deposed Iraqi leader Saddam Hussein. But placing the responsibility solely on Bush's shoulders is too simple and even potentially dangerous. Too simple, because it blurs the responsibilities of those outside the administration who contributed to an environment where bad new ideas were embraced just as quickly as good proven ones were shed. The promise that a tsunami of democracy would spread from Iraq to its neighbors, for example, was as poorly scrutinized as the notion that the Geneva Conventions need not “apply precisely” in Iraq. Blaming Bush alone is also dangerous, because without a clearer understanding of how this permissive intellectual environment emerged, a future U.S. administration could again exploit the public fear instilled by terrorism to let unfounded assumptions guide ill-fated interventions abroad.

In the coming years, challenges similar to those posed by Iraq will surely surface elsewhere. The world hardly lacks for tyrants willing to challenge Washington, and Iraq will not be the last instance in which foreign powers oust a dangerous regime or in which outsiders play some governing role as a collapsed state regains its footing. Moreover, further terrorist attacks in the United States remain probable. These factors may recreate a public mood where the urge to “do something” weakens the quality control of a superpower's policy decisions.

Today, few doubt that the Bush administration's postwar planning was disastrous. Insiders' books, congressional testimony, and recent investigative reporting indicate that the miscalculations resulted from a toxic combination of ideology, terrorism, and an...