Assassinations cast a long shadow on the history of the United States. Presidents, Congressmen, governors, mayors, state legislators, judges, and other prominent public figures all have been the targets of disturbed or fanatical individuals bent on murder as an expression of their real or imagined grievances. After every such occurrence, the press and the public express shock and demand explanations, hoping that an analysis of the cause may serve to prevent future killings, or at least help to develop better means to protect potential targets in the future. "Assassination and Political...