Mitt Romney’s enduring problem is that we don’t know what lies beneath the eager-to-please demeanor that leads him to emit impenetrable lines like the one this weekend about loving Michigan because its “trees are the right height.”

This creates a vacuum that inevitably gets filled with morsels of insight like the old story about his onetime dog, Seamus. In a web ad deployed last month during the South Carolina primary, Newt Gingrich resurrected a 2007 Boston Globe article telling the tale of how Romney strapped the family’s Irish setter to the roof of the car for a 12-hour drive to Canada. According to the candidate’s son Tagg, stops were carefully calculated to allow the hound to answer the call of nature, but Seamus didn’t get the memo. Dad calmly pulled into a gas station, hosed down the dog, the car and the crate, and the terrifying ride resumed.

The son apparently shared the anecdote as an illustration of his father’s gifts as an emotion-free crisis manager. But grace under pressure isn’t the image of the former Massachusetts governor that emerged with the retelling. Much in the same way John Edwards came to rue his $400 haircut, and John McCain had trouble living down his inability to count the number of houses he owned, Seamus dogs Romney.

Late-Night Fodder

The story has at least four legs. “Saturday Night Live” recently featured Seamus in a skit; it’s a running joke on David Letterman’s late-night show; and a parked car with a big stuffed dog on top routinely shows up at the candidate’s rallies. Fox News’ Chris Wallace joined the New York Times columnist Gail Collins in expressing incredulity. “I have a yellow Lab named Winston,” Wallace said to Romney. “I would no sooner put him in a kennel on the roof of my car than I would one of my children.”

Romney insists Seamus loved his crate and appreciated fresh air, even at 60 miles per hour. That hasn’t appeased Dogs Against Romney, a group whose human founder, Scott Crider, is trying to get word out to the country’s 43 million dog owners, who represent all political breeds. Dogs Against Romney, which had more than 1 million visitors to its website in its first 10 days, recently organized an anti-Romney protest at the Westminster dog show. It also awarded a congratulatory “woof” to Lanny Davis, a former special counsel to President Bill Clinton, who wrote in The Hill newspaper that a man who would insist his dog enjoyed such abuse is unfit to be president.

Although Romney says Seamus lived happily ever after on a farm, New York Observer blogger Hunter Walker reported that two of the Romney sons had said the dog ran away upon reaching Canada. This tale of seeking asylum with our good neighbor makes sense when you consider the possibility that Seamus may have picked up some French from his master, who performed more than two years of Mormon missionary service in France as a young man.

Zut alors! It was only a matter of time before the Obama re-election campaign saw a puppy in the manure. A few weeks ago, the chief strategist, David Axelrod, put a picture on Twitter of the president scratching the neck of his dog, Bo, who was sitting in the plush back seat of the presidential limo. The caption: “How loving owners transport their dogs.”

The White House website is a shrine to all things Bo (“Meet Bo,” “Bo’s First Month,” “Bo: The Photo Gallery”) and he makes the perfect campaign surrogate. With a dog, there’s no risk of evoking the kind of complicated family tableau that appears when Gingrich’s daughters from his first marriage defend him against accusations the second wife has made about the third.

Silent Partner

Nor is a dog about to blunder like Foster Friess, the fundraiser whose comments added fuel to the furor over Rick Santorum’s controversial views on insurance coverage for contraceptives. It took days for Santorum to stop the snickers after Friess told NBC’s Andrea Mitchell that in his day an aspirin squeezed between the legs served as cheap and accessible birth control.

Santorum has his own canine problem -- his comments comparing homosexuality to “man on dog” still get more attention than the legislation he sponsored in the Senate to regulate scandalous puppy mills -- and he shouldn’t try to go paw to paw with Bo. The cuddly Portuguese waterdog is never going to make a bad joke. He has no record to explain, no earmarks to disavow, no insider status to hide because much of his business takes place outdoors, even if he does live in the White House.

Bo’s Everycanine is better at humanizing a candidate than props such as Joe the Plumber, who ruined things as soon as he opened his mouth. The First Hound isn’t the least bit aloof and has no intellectual pretentions.

Seamus is another story. His travails resonate because, despite all the debates, position papers and campaigning, voters don’t know much about Romney. He comes to us largely in gauzy ads, protected by a cocoon of advisers whose greatest fear is that he might reveal himself. There are so many things that might humanize the candidate and that he won’t discuss: How being a Mormon shapes his worldview; how it felt to close businesses while at Bain Capital LLC; what it was like for a Republican to govern a state as blue as Massachusetts; what he feels when a maid without health insurance is cleaning his hotel room; what movies make him laugh or cry.

As long as we’re left to guess about so much, it’s easy to fill the void about what’s inside the man with the story of the dog he left outside.

(Margaret Carlson is a Bloomberg View columnist. The opinions expressed are her own.)

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To contact the writer of this article: Margaret Carlson at mcarlson3@bloomberg.net.

To contact the editor responsible for this article: Max Berley at mberley@bloomberg.net.