It is only now, nearly five years after Sept. 11, that the full picture of the Bush administration’s response to the terror attacks is becoming clear. Much of it, we can see now, had far less to do with fighting Osama bin Laden than with expanding presidential power. Over and over again, the same pattern emerges: Given a choice between following the rules or carving out some unprecedented executive power, the White House always shrugged off the legal constraints. Even when the only challenge was to get required approval from an ever-cooperative Congress, the president and his staff preferred to...