GOP presidential hopeful Mitt Romney might be the big dog on the campaign trail, but his stock among the friends of the four-legged continues to falter because of the persistence of infuriated animal lovers who refuse to let die the story of the Romney family pet’s harrowing 1983 car ride.

“They say if you want a friend in Washington, get a dog. If that is true, what would Mitt Romney do if he won?” Dogs Against Romney spokespup “Rusty” posited to Heard on the Hill.

The traumatizing trip that continues to raise Rusty’s hackles was uncovered by Boston Globe Magazine scribe Neil Swidey, who unearthed the story about the more than 12-hour commute from Boston to Canada that Romney’s since-deceased Irish setter, Seamus, endured in a custom pet carrier strapped to the roof of the family vehicle.

Swidey broke that story June 27, 2007. Three days later, social media savant Scott Crider took up the mantle and kicked off his anti-Romney campaign with dogsagainstromney.com.

The website was dormant until early 2011, at which point pet owners sympathetic to Seamus’ plight began posting pics of their own furry family members punctuated by anti-Romney missives.

The online ribbing has graduated to the pinnacle of do-it-yourself politicking — merchandising — and now includes bumper stickers and T-shirts declaring: “Mitt Is Mean,” “I Ride Inside” and “Never Forget Crate-Gate.”

The group has also taken a page from Savage Love author Dan Savage, lobbying to redefine “Romney” as: to defecate in horror.

Why? Among the gems in Swidey’s reporting was that Romney’s son, Tagg, noticed that a “brown liquid” was streaming down the back window during the trip to Canada, and it was coming from Seamus.

Although he’s racked up more than 18,000 Facebook “likes” and 2,000-plus Twitter followers (@Grrr_Romney), Crider said the Romney camp remains incommunicado about his efforts.

Should Romney fall short of claiming the White House, Crider suggested he’d be inclined to retire virtual watchdog “Rusty.”

“If meanie Mitt Romney wins, I will keep dogging him. Grrr,” he pledged.