Law enforcement officers are public servants. Taxpayers foot the bill for their salaries, equipment, and sometimes their peccadilloes (or at least legal settlements). Police officers belong to public-sector unions, like other public servants. But police unions are not like those other unions, just as police are different from the often faceless bureaucrats who keep state and local governments running.These differences are starkly illustrated in the grudge match between the New York Police Department and New York Mayor Bill de Blasio.The fight is national news: Egged on by their unions &mdash...