Last week’s furore over the US senate’s report into the CIA’s torture of detainees was a reminder that since 9/11, America’s decision-makers have been a little like Darren Wilson, the Missouri policeman who shot and killed the unarmed black teenager Michael Brown last August. By his own account, Mr Wilson had been mortally afraid. Brown, he said, “looked like a demon”, and he feared the young man might punch him to death. In his own mind therefore, he had acted in self-defence when he shot Brown dead. The 2001 terror attacks left US leaders making decisions in a climate of...