Today should be a moment of celebration for Mitt Romney’s presidential campaign. Not only did he cruise to victory in the Illinois primary on Tuesday night but he received the endorsement of former Florida governor Jeb Bush today.

Instead of rejoicing in what looks to be the beginning of the end of the Republican presidential race, however, Romney and his team are on the defensive over an Etch-a-Sketch. Yes, an Etch a Sketch.

Erik Fehrnstrom, one of Romney’s top aides, made the unfortunate comparison between his candidate and the child’s toy during a television interview on CNN on Wednesday morning.

“Well, I think you hit a reset button for the fall campaign,” said Fehrnstrom. “Everything changes. It’s almost like an Etch a Sketch – you can kind of shake it up, and we start all over again.”

Cue outrage.

Both former Pennsylvania senator Rick Santorum and former House Speaker Newt Gingrich could immediately be seen toting Etch a Sketches on the campaign trail — a visible (and inexpensive!) symbol, they argued, of Romney’s lack of core conservative convictions. A Santorum aide was handing out mini Etch a Sketches to reporters at a Romney event this afternoon in Maryland.

Democrats immediately pounced on Fehrnstrom’s Etch a Sketch moment too. The Democratic National Committee sent 16 separate emails to reporters highlighting the comment and even produced a web video mocking it:

The Romney campaign quickly sought to play defense. “As we move from the primary to the general election, the campaign changes,” spokeswoman Andrea Saul said. “It’s a different race, with different candidates, and the main issue now becomes President Obama’s failure to create jobs and get this economy moving.”

How you view the Etch a Sketch incident — kind of has a ring to it, no? — depends in large part on how you view Romney.

If you are favorably disposed to Romney (and Fehrnstrom) you dismiss this episode as simply the latest example of how the media focuses on all the wrong things.

If you don’t like Romney, you see Fehrnstrom’s comment as a rare moment of candor from a campaign — and a candidate — who will say and do anything to win.

Viewed as objectively as possible, however, what this episode highlights is how small things in modern politics can — and often do — become big things.

Swiss cheese on a cheesesteak. Uncertainty about how many houses you own. Corporations are people too. Windsurfing as a pastime. Curt Schilling as a Yankees fan. And those are just the handful we thought of off the top of our heads.

In a world driven by viralness and social media, small things can grow to be big things very quickly. One recent example: A video mashup of things Romney has said on the campaign trail set to the tune of Eminem’s “The Real Slim Shady” had 300 views on You Tube when we saw it on Tuesday morning. It has more than 900,000 hits now.

Small things are also often seen by voters as a window into the true nature of a candidate or a campaign. It wasn’t that John Kerry ordered swiss cheese on his cheesesteak; it was that in so doing he proved he wasn’t a regular guy. It wasn’t that George H.W. Bush seemed to be amazed at a grocery scanner; it was that it affirmed that he was out of touch with the pocketbook concerns of regular people.

Which brings us back to the Etch-a-Sketch incident. What Fehrnstrom actually meant doesn’t matter at this point. The Etch a Sketch line will now have a life of its own that will continue to be a sore spot for Romney and his campaign for the foreseeable future. (Can you really see a scenario where Democrats drop it entirely? We can’t.)

One sentence about an Etch a Sketch isn’t going to decide whether Romney will be the Republican presidential nominee (he almost certainly will) or whether he can beat President Obama in the fall.

But, it’s one more piece of evidence that Democrats will use to paint Romney as a politician’s politician — willing to say whatever he thinks the audience he’s in front of wants to hear.

And that’s why it matters.