As the nation's "drug czar," John Walters is supposed to be saving us from the ravages of hard drugs like heroin and cocaine. At least that was the original sales pitch for the "war on drugs" in the 1980s. But the war has evolved into largely a fight against marijuana, which no one has ever claimed is a hard drug. Walters is nonetheless committed, Ahab-like, to arresting every marijuana smoker in the country whom law enforcement can lay its hands on. It used to be that drug warriors denied that marijuana was much of a focus for them, because they...