Mike Maharrey untangles the complex web of legal history that has given America the system known as qualified immunity, which in practice shields police officers from just about any civil lawsuit. The doctrine, which has emerged out of the precedents set by repeated federal court rulings, makes it almost impossible to sue state agents for constitutional violations or other damages suffered during the performance of their jobs. This is mainly because the courts have decided that unless there is specific precedent for the situation the officer finds himself in, discretion must be left up to...