Try this thought experiment: You decide to donate money to Mitt Romney. You want change in the Oval Office, so you engage in your democratic right to send a check.Several days later, President Barack Obama, the most powerful man on the planet, singles you out by name. His campaign brands you a Romney donor, shames you for “betting against America,” and accuses you of having a “less-than-reputable” record. The message from the man who controls the Justice Department (which can indict you), the SEC (which can fine you), and the IRS (which can audit you), is clear: You made a mistake donating that money.Are you worried?Richard Nixon’s “enemies list” appalled the country for the simple reason that presidents hold a unique trust. Unlike senators or congressmen, presidents alone represent all Americans. Their powers—to jail, to fine, to bankrupt—are also so vast as to require restraint. Any president who targets a private citizen for his politics is de facto engaged in government intimidation and threats. This is why presidents since Nixon have carefully avoided the practice.Save Mr. Obama, who acknowledges no rules. This past week, one of his campaign websites posted an item entitled “Behind the curtain: A brief history of Romney’s donors.” In the post, the Obama campaign named and shamed eight private citizens who had donated to his opponent. Describing the givers as all having “less-than-reputable records,” the post went on to make the extraordinary accusations that “quite a few” have also been “on the wrong side of the law” and profiting at “the expense of so many Americans.”These are people like Paul Schorr and Sam and Jeffrey Fox, investors who the site outed for the crime of having “outsourced” jobs. T. Martin Fiorentino is scored for his work for a firm that forecloses on homes. Louis Bacon (a hedge-fund manager), Kent Burton (a “lobbyist”) and Thomas O’Malley (an energy CEO) stand accused of profiting from oil. Frank VanderSloot, the CEO of a home-products firm, is slimed as a “bitter foe of the gay rights movement.”