After the 9-11 Attack, the United States united under a single cause: the fight against terrorism. While this is a good objective, it needs to be achieved in a careful manner, while respecting constitutional principles.
The War on Terror and the Iraq War commited many mistakes, and violated many constitutional principles. For example, the Iraq War was initiated without enough justification. Mass hysteria made it possible for the government to bypass these problems more easily, because it made the American public more complacent.
