The last week has given us lessons from both ends of the authenticity spectrum. First, Hillary Clinton, received in the New York Times Magazine her first big campaign profile of the season, and the takeaway is her perpetual struggle to show voters her “real” self. Even before her campaign officially began, Clinton labored to beat back a revival of the old criticisms that plagued her in 2008 and during her White House years: that she’s defensive and unrevealing in her public speech; that she chooses her political positions according to the polls, not conviction; that she dons and doffs personas as often as hairstyles. Hillary is, in short, the latest in a line of White House aspirants—Mitt Romney, Al Gore, John Kerry and a dozen lesser lights—with an authenticity problem.

Of course, the other big campaign “story” this week—and the scare quotes are, sadly, necessary—wasn’t about Hillary but rather the campaign’s other tonsorially challenged front-runner, Donald Trump. For weeks Trump has offered the American electorate a crash course in authenticity. Apparently intoxicated by the empyrean heights in the polls where he suddenly found himself, he has in recent days unaccountably impugned John McCain’s heroism, called several of his rivals stupid and shared Lindsey Graham’s personal cellphone number with the Internet. In case there was any lingering doubt about the showman, it’s clear now to every potential voter that Trump is nothing but himself.

For many election cycles now, Americans have pined for a straight-talking, truth-telling, spontaneous, unpackaged, unrehearsed savior to redeem our vapid, scripted politics. We have yearned for someone not only honest with us but true to himself or herself—someone not only sincere but authentic. (Sincerity exists between two people; authenticity exists within one.) To judge their authenticity, we want access to their true selves, which we think comes from sharing in their private, personal and family moments.

It’s tempting to conclude that this desire is a response to the tedious superficiality and homogeneity of our contemporary politics—the reign of the consultants, who feed their clients mass-produced phrases from one election to the next; the power of the polls, which like flares on a runway, warn politicians not to stray from the straight and narrow; the ubiquity of the news media, who festoon the campaign trail with trip wires and then fault the candidates for tiptoeing around them.

But our collective expectation that candidates should share with us their true selves—their personality, their humor, their opinions about baseball teams or movie stars, information about their families or their upbringing—is not a particularly recent phenomenon. It dates at least to the early 20th century, when candidates first began traveling the country to win votes and spending zillions on advertising (comparatively, at least), and when presidents first began using the mass media to win public support for their agendas. ...