All political gaffes are not created equal.

Some come to define campaigns, others disappear in a single news cycle (or sometimes less).

Photo illustration by Allie Ghaman/The Washington Post; original images by AP/Ohio Art and Melina Mara/The Washington Post

So what differentiates the gaffes that enter campaign folklore from those that even the most committed political junkies struggle to recall even a few weeks after they happen?

It’s actually a relatively simple answer: Gaffes that matter are those that speak to a larger narrative about a candidate or a doubt/worry that voters already have about that particular candidate.

Take the gaffe du jour — Mitt Romney aide Erik Fehrnstrom’s reference to an Etch-a-Sketch when asked whether the former Massachusetts governor’s move to the ideological right in the primary would hurt him with general election voters.

The Etch-a-Sketch incident is likely to linger in the electorate because it speaks to a broader storyline already bouncing around the political world: That Romney lacks any core convictions and that he will say and do whatever it takes to win. (It IS worth noting that Romney didn’t say the Etch-a-Sketch line — making it less powerful and perhaps less long lasting.)

Romney is also not helped by the fact that the Etch-a-Sketch is such a fun — and cheap! — campaign prop. Already both former House Speaker Newt Gingrich and former Pennsylvania senator Rick Santorum have been seen sporting Etch-a-Sketches on the trail. And you can bet Democrats are buying the children’s toy in bulk today for future use. (Not surprisingly, Etch-a-Sketch stock has soared over the past 24 hours.)

To that point, the Democratic National Committee released their second Etch-a-Sketch web video in as many days:

Contrast Fehnstrom’s gaffe with President Obama’s slip-up in May 2008 when he told a crowd in Oregon: “Over the last 15 months, we’ve traveled to every corner of the United States. I’ve now been in 57 states?”

Conservatives insisted that the reason that gaffe didn’t get enough attention was because of the media’s favoritism directed toward Obama. But, the truth is that the “57 states” comment didn’t become a defining moment in the 2008 campaign because there was no “Obama isn’t smart enough to be president” narrative out there. Democrats, independents and even many Republicans agreed that Obama had the intellectual goods to be president although there was considerable disagreement about whether his policies were the right fit for the country.

While Obama’s “57 states” gaffe never caught on, his comments about rural voters “clinging” to their religion and their guns — made at a fundraising event in California — became a huge problem for his campaign. Why? Because there was an “Obama as elitist” narrative already in the political bloodstream that his “cling” comments played directly into.

Recent (and even not-so-recent) political campaigns are filled with gaffes that prove our point.

* Massachusetts Sen John Kerry’s order of swiss cheese on his cheesesteak mattered because he was already fighting against the idea that he was out of touch with average Americans.

* Rick Perry’s “oops” moment mattered because from the second the Texas governor announced his 2012 candidacy for president there were questions about whether or not he was up to the task.

* George H.W. Bush looking at his watch during a presidential debate in the 1992 campaign mattered because there was a already a sense in the electorate that the incumbent president was aloof and uncaring.

* Edmund Muskie’s tearing up in New Hampshire during the 1972 presidential campaign mattered because it reinforced the idea kicking around in political circles that he was emotionally unstable and prone to burst of temper. (The one and only David Broder wrote extensively about the Muskie crying episode in his book “Behind the Front Page”.)

Playing to type — or even appearing to play to type — is the kiss of death when it comes to political gaffes. Given that political reality, Ferhnstrom’s Etch-a-Sketch gaffe looks likely to hound Romney for the foreseeable future.