If you aren’t old enough to remember it, you’ve probably heard the story of the most consequential presidential campaign gaffe of the modern era. In 1972, Maine Sen. Edmund Muskie responded to a series of attacks by the Manchester Union Leader with a news conference outside the paper’s offices. Standing in the New Hampshire snow, the candidate for the Democratic nomination condemned the paper for, among other things, attacking his wife. The Washington Post’s David Broder began his story about the incident this way: “With tears streaming down his face and his voice choked with emotion . . .” 

Though Muskie insisted that his facial wetness came from the snow, the idea that a candidate would cry created a scandal. Muskie, thought until that moment to be his party’s inevitable nominee, soon saw his campaign flounder and die.

The less well-known part of this story is that some influential journalists had decided long before that there was something slightly off about Muskie. In his 1977 book “Reporting: An Inside View,” legendary journalist Lou Cannon wrote that, after playing poker with Muskie, he concluded that the senator was too temperamental to be president. “What does a political reporter do with this kind of insight?” Cannon asked. “As in this instance, it is rarely written as a hard news story the first time the thought arises. . . . What we reporters tend to do is to store away in our minds such incidents and then use them to interpret — to set a context — for major incidents when they occur.” 

What makes an incident or gaffe “major” is the interpretation that journalists — and these days, the blogosphere and Twitterverse as well — give it. Some mistakes are largely ignored, while others are portrayed as enormously consequential and haunt the candidate for weeks or months. The difference reveals far more about journalistic biases than it does about the candidates themselves. 

In every campaign, candidates’ verbal miscues draw plenty of attention, and the GOP primary race this year is no different. At a stop in Iowa on Thursday, Mitt Romney blurted out that “corporations are people” and engaged in a mini-debate on the issue with the crowd. In recent weeks, Newt Gingrich came under heavy criticism for describing Republican Rep. Paul Ryan’s Medicare plan as “right-wing social engineering.” Tim Pawlenty referred to the Affordable Care Act as “ObamneyCare,” then backed down when asked to repeat it to Romney’s face in a nationally televised debate. And Michele Bachmann has been caught in a series of factual errors, such as placing the Battles of Lexington and Concord in New Hampshire rather than Massachusetts; claiming her birthplace of Waterloo, Iowa, as the home of John Wayne, when it was actually serial killer John Wayne Gacy who hailed from there; and asserting that the founding fathers “worked tirelessly” to eliminate slavery.

All of these misstatements had something in common: They reinforced what many people — including reporters — already thought about the candidate in question. That’s why the incidents became “news.” 

In Gingrich’s case, reporters have long believed him to be undisciplined and erratic. Romney is supposed to be not only a creature of big business but inauthentic as well, awkwardly trying to ingratiate himself with voters. (Sometimes derided as “Romneybot,” he’d be the one to see no difference between corporations and human beings.) Pawlenty is thought by some to be unprepared for the hardball of a presidential campaign, while Bachmann is considered an intellectual or policy lightweight — a “flake,” as Chris Wallace so ungraciously said to her on “Fox News Sunday.”

The politicians’ so-called gaffes don’t tell us anything new. Instead, they allow reporters to explain how what they’ve thought all along about a candidate is true. 

You know a gaffe has made its mark when it becomes the subject of late-night monologues. Stewart and Colbert offer biting satire of the candidates, while Leno, Letterman, Fallon and O’Brien deal in broad strokes — but all tend to focus on one or two characteristics of each major political figure, and nearly every joke becomes a variation on that theme. John McCain was a grumpy old man, George W. Bush was dumb, John Kerry was a stiff patrician, Al Gore was dishonest and self-aggrandizing. Every politician is defined by what is allegedly his or her biggest character flaw.

If the candidate’s misstep doesn’t hew to the stereotype, chances are it’ll be soon forgotten. During a 2008 stop in Oregon, then-Sen. Barack Obama noted that he had visited “57 states” during his presidential campaign. Despite the efforts of some GOP partisans, the mainstream media quickly moved on; most journalists assumed Obama knew the right number and had simply misspoken. Today, if Bachmann says something that sounds like an awkward attempt to ingratiate herself with voters, reporters won’t speed-dial their editors. If Romney makes a factual error about the founding fathers, it will be greeted with a yawn. He’s supposed to be the insincere one without a handle on human interaction, and she’s supposed to be the dolt.

The result is profoundly unequal treatment of candidates. Get branded as dishonest, and reporters will pore over your statements to see if you’ve ever strayed from the truth; if they find that you have, they’ll assume it was an intentional deception and not a mistake. (Just ask Gore, who never actually claimed that he invented the Internet.) Get a reputation as a fool, and the same error will be presented as yet more evidence that you lack the intellect for whatever job you’re seeking. 

There’s nothing partisan about it. Think about the 2008 election. When McCain was unable to recall how many houses he owned, the stories about it were as good a mark as any that the character judgment reporters were making about him had shifted. No longer the much-admired “maverick,” McCain had become just another rich, out-of-touch Republican. But his opponent got off no easier: When Obama was secretly recorded saying that white working-class voters in the Rust Belt, in the face of their economic struggles, “cling to guns or religion,” it allowed reporters to place him in the stereotype of Democrats as cultural elitists. Both episodes became major stories.

These gaffes rarely concern substantive policy issues — in fact, the less they are about policy, the more likely they are to stick. Mischaracterize your opponent’s tax plan and observers will barely bat an eye, but pad your résumé, and your fundamental character will be questioned.

And of course, “character” is the primary theme of all campaign coverage — not what candidates will do once they take office, but who they are deep within. The gaffe is supposed to reveal this inner character, to strip away the carefully crafted veneer and show the real person. And sometimes it can.

But it’s hard not to feel for the candidates. Imagine if every day for the next year, you had to deliver five or six extemporaneous speeches and make small talk with hundreds of strangers, all while people followed you around recording every word.

Chances are you’d say a few things you’d like to take back. Those mistakes might reveal who you really are. But more likely, they’d reveal who the person holding the microphone or notebook or camera thinks you are.

Paul Waldman is a senior correspondent for the American Prospect and the author of “Being Right Is Not Enough: What Progressives Must Learn From Conservative Success.”

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Journalist Paul Waldman explains how politicians’ missteps go viral