It might be unseemly to bring this up just as Mitt Romney celebrates his win in New Hampshire on Tuesday night and seems to be a strong front-runner for the GOP nomination. But the story of his putting his dog in a carrier on his car roof for a 12-hour family trip is spreading again on the Internet and disturbs me the more I learn about it.

And I am betting the more it gets out, the more votes Romney loses — red, blue and purple.

When, in a campaign debate, Romney opposed allowing a non-documented worker who has lived here for 25 years to stay and earn his way to citizenship, he struck me as heartless.

But when I read the story recently in greater detail about what Romney did to his Irish Setter, Seamus, that struck me as more than heartless — it struck me as downright cruel.

In brief, as The Boston Globe first reported in 2007, in 1983, Mitt Romney, then 36 years old, drove his station wagon packed with five sons and his wife on a 12-hour trip from Boston to Ontario, where his parents had a cottage on Lake Huron.

He took a dog carrier and attached it to the station wagon’s roof rack, built a special windshield and put his dog Seamus into the carrier, where the dog remained for the 12-hour trip.

Was the dog distressed? Was it illegal under Massachusetts law as cruelty? There is some evidence that both are true.

During the trip, The Boston Globe reported, Romney’s oldest son, Tagg, looked around through the rear window and yelled, “Dad — gross!” A brown liquid was dripping down the back window — diarrhea from an animal that just might have been caused by the stress of being inside a cage for 12 hours on top of a car going 60 mph.

And what did Romney do, even after knowing of the dog’s diarrhea? Did he realize that perhaps Seamus should be shown some mercy, cleaned up and allowed in the car, to sleep on someone’s lap?

No.

Here’s how The Globe described what Romney then did:

“As the rest of the boys joined in the howls of disgust, Romney coolly pulled off the highway and into a service station. There he borrowed a hose, washed down Seamus and the car, then hopped back onto the highway. It was a tiny preview of a trait he would grow famous for in business: emotion-free crisis management.”

Emotion-free crisis management??!

I love animals, especially dogs. I don’t like people who are cruel to animals. I am told it is illegal in Massachusetts to put an animal on a car roof while driving. Had I been the local sheriff, I would have arrested him.

But I am a forgiving person. If today Romney, looking back, were to say, “You know, in retrospect, that was a cruel thing to do to our dog — I was young, it was a long time ago, I am sorry” — if he said that today, I’d forgive him.

But instead — Romney being Romney — he defaults into saying something utterly implausible. He recently told Fox’s dog-loving Chris Wallace that Seamus actually loved it up there!

He then told Wallace that the dog was in an “air-tight container,” not mentioning the diarrhea.

Air-tight container??!

This is the ultimate Purple Issue — it cuts across Republicans, Democrats, blue states, red states, liberals and conservatives.

There are more than 78 million Americans who own one or more dogs — about two out of every five households. A Google search of “Romney Dog on Car Roof” brought me 1,080,000 results.

I don’t know how many of these 78 million dog owners (and thus, dog lovers) have yet heard or read about Romney doing this horrible thing, much less making his disingenuous claim that Seamus loved the experience on top of a speeding car for 12 hours, while his bowels turned to water.

But I’m thinking if this story gets out and stays out, there will be tens of millions of Google hits by next October. And I am also thinking that Romney is going to lose a lot of dog-lover votes on this issue alone, regardless of party or ideology.

Here’s one dog lover’s opinion — mine:

I think anyone who puts his dog in a cage on top of a car for a 12-hour drive and then deludes himself or tries to delude others that the dog really enjoyed it — to me, with all due respect, I feel such a man shouldn’t be president of the United States.

Lanny Davis is the principal in the Washington D.C. law firm of Lanny J. Davis & Associates, which specializes in strategic legal crisis management. He served as President Clinton’s Special Counsel in 1996-98 and as a member of President Bush’s Privacy and Civil Liberties Oversight Board in 2006-07. He is the author of the forthcoming book to be published by Simon & Schuster, “Crisis Tales — Five Rules for Handling Scandals in Business, Politics and Life.” He can be found on Facebook and Twitter (@LannyDavis).