Catherine Engelbrecht’s tale has all the markings of a classic conspiracy theory: She says she thinks that because of her peaceful political activity, she and her family was targeted for scrutiny by hostile federal agencies. Yet as news emerges that the Internal Revenue Service wielded its power to obstruct conservative groups, Catherine’s story becomes credible — and chilling. It also raises questions about whether other federal agencies have used their executive powers to target those deemed political enemies. Before the Engelbrecht family’s three-year ordeal began, Catherine says, “I had no real expectation or preparation for the blood sport that American...