It’s an anti-Romney movement five years in the making, and now it’s a large and growing “Super Pack” that even plans to crash the legendary Westminster Kennel Club Dog Show this week.

Dogs Against Romney is an ad-hoc group that likes dogs (and even, when pressed, some cats) but does not like Mitt Romney. It was brought together by the now well-known story of how Romney, the Republican presidential candidate, once drove from Boston to Canada with his dog in a carrier strapped to the roof of the speeding family car.

For those unfamiliar, the story –- unearthed by the Boston Globe in 2007 — goes something like this: In 1983 Romney, then a rising star in the private equity world, loaded up the family station wagon with sons and luggage for a long trek from Boston to Ontario, Canada. Seamus, the family’s Irish Setter, was put in his dog crate and strapped to the top of the car. Poor Seamus, whether terrified or over-excited or just not given a chance for a potty break, at some point soiled himself, as the Romney boys discovered when they saw brown liquid running down the window. Romney, the turnaround and efficiency specialist, quickly pulled into a nearby gas station to hose down the car, and the dog, and get back on the road.

Not long after the Seamus story became public, dog lover Scott Crider started the dogsagainstromney.com website and blog, in time for the former Massachusetts governor’s first, unsuccessful White House run. With Romney now arguably the Republican front-runner for 2012, the website and the movement have returned with fresh vigor.

Crider, 47, is a digital creative director and social media strategist based in Gulf Shores, Alabama, who works on the website in his spare time. He calls it “a work of satire with a serious message, and totally grass-roots.” The generic brown dog — nicknamed Rusty –- in the current stars-and-stripes emblazoned “In Dog We Trust/Dogs Against Romney” poster is “a composite of all the dogs I’ve owned in my life,” said Crider.