CLEVELAND >> In Florida, a state trooper pulled Jim Wilson off the highway, but instead of issuing a speeding ticket, asked a favor: Could he have a few Romney for President bumper stickers?

In Michigan, a woman left a handwritten letter for Mitt Romney on Wilson’s dashboard, recounting her husband’s trouble finding work. “We pray you can get us out of this mess,” she wrote.

And here in Ohio, three young men surrounded Wilson’s car, repeated an anti-Romney chant and broke his driver’s side windshield wiper.

The cocoonlike machinery of the modern presidential campaign, with its bulletproof motorcades, private planes and handpicked audiences, has kept Romney largely insulated from the public’s raw reactions to his candidacy.

The same, however, cannot be said for his most fanatical supporter, a 69-year-old former life insurance salesman and an unabashedly anti-Obama Republican from Virginia.

For the past year, Wilson has devoted himself with the single-mindedness of a college-age groupie to following Romney around the country in decidedly conspicuous style: driving a pickup truck festooned with 27 giant Romney for President posters. (The largest are the size of a refrigerator.)

Forgoing home-cooked meals and forbearing horrendous traffic, he has driven, sometimes nonstop, from Omaha, Neb., to Charlotte, N.C., (19 hours), Portsmouth, Va., to Tampa, Fla., (14 hours) and Des Moines, Iowa, to Manchester, N.H., (22 hours), showing up, almost without fail, just in time to greet guests outside of a Romney event.

In the process, Wilson and his truck have become a kind of mobile barometer of the candidate’s popularity, or lack thereof, in an era of hyper-partisanship.

There were the workers in Detroit, who he said backed a garbage truck into to his white 1998 extended-cab GMC 1500, leaving an ugly gash. There was the woman in Illinois who tearfully handed him a plastic rosary, intended as a gift for Romney. And there were the tomatoes splattered across his windshield.

“I don’t remember which state that was, but I know they were ripe, so it must have been the South,” Wilson said during an interview from inside his truck, as it rumbled across Ohio not long ago.

Mostly, though, the feedback can be broken down into two categories: a raised thumb or an outstretched middle finger. “These days,” he said, “the thumbs up are vastly outnumbering the third digits. I like that.”

To those who contend that Romney does not inspire the same kind of deep-seated, drop-everything dedication as, say, Barack Obama in 2008, Wilson is a four-wheel rebuke. Since last summer, he has logged about 40,000 miles, visited 15 states and attended 150 campaign events on Romney’s behalf.

“I don’t think anyone has as much sweat equity in this sucker as I have,” Wilson said.

He made the decision to spend 11 months of his life shadowing Romney on something of a whim. In July, he met the former Massachusetts governor at the Iowa State Fair, terrain that Wilson knew well from growing up on a hog farm in the state, where his father and grandfather had been active in Republican politics. He had dabbled in campaigns himself, mostly in Virginia, as a volunteer.

He liked what Romney had to say about free enterprise and federal regulation, and he could never muster much interest in Newt Gingrich (“his time has passed”) or Rick Santorum (“a little whiny”). But more than anything, he hated what he believed Obama stood for: big government run amok.

“I mean, is there no facet of our government into which this president has not poked his nose or hands?” he asked.

On the cusp of his eighth decade, with his finances secure, no family at home and health intact, Wilson realized something else. This could be his last political campaign. So why not go out with a bang?

A Vietnam veteran whose legal name is Norris Aubrey Wilson II, he is an unlikely mascot for the buttoned-up, rules-obsessed Romney. Wilson is frequently profane (cycling through jokes about weight, Viagra and Rogaine), smokes a pipe, carries a fish-skinning knife with a three-inch blade and dons an almost cartoonishly retro wardrobe of knee-high tube socks, bright white sneakers and “Magnum P.I.”-era Tom Selleck beige shorts.

The Romney campaign kept its distance from him at first. Aides to Romney, nervous that a suddenly ubiquitous fan might prove a liability, went so far as to vet him. Finding nothing alarming, they began to see an upside to his doggedness and free labor.

They gave him lawn signs and bumper stickers to hand out. They enlisted him to direct traffic at events. And they sent him regular updates on their schedule.

Over time, he has become unexpectedly valuable to the campaign: a highly recognizable landmark for drivers trying to find an event; tangible evidence of Romney’s down-home appeal; and, perhaps most important, an accessible, garrulous and charming counterpoint to a sometimes awkward candidate.

Will Ritter, who oversees a team that organizes events for the Romney campaign, compared Wilson and his truck to “balloons around the mailbox at a birthday party, letting you know you’re at the right place.”

In Tampa, a local Republican organizer approached Wilson with a complaint: She could not get her hands on Romney lawn signs.

“You have to steal them,” Wilson deadpanned.

He then promised to look into the problem and gave her a bear hug. “I don’t shake hands with girls,” he explained, as her husband looked on, quizzically. “Girls are made for hugs.”

Outside an event in Westerville, Ohio, Wilson tried to persuade an Obama supporter to give Romney a shot.

“I just don’t find him to be genuine,” the man insisted.

Wilson nodded politely, then made his pitch. “We tried Obama,” he said, “but that didn’t work.” The men shook hands, agreeing to disagree.

For many campaign volunteers, the reward for long hours is face time with the candidate. Wilson seems uninterested, repeatedly turning down invitations to meet with Romney backstage at events. They mostly exchange waves.

Wilson does not shy from criticizing the campaign, at times in punchy emails to staff members. He thinks the candidate needs to loosen up a little. He wishes aides would step up outreach to veterans. And he wants Romney to spend less time on the East Coast.

“He’s got to get out West,” Wilson complained a few days ago as he smoked beside his truck in Jacksonville, Fla.

On the trail, Wilson lives sparingly. Whenever possible, he stays at a Motel 6 because it’s inexpensive and the chain lets him to smoke in his room, unlike the Marriott hotels that Romney favors. “They’re Mormons,” he said of the Marriott family. “That’s fine.”

He subsists on raw almonds, sliced deli meat, yogurt and Diet Coke, which he stores in coolers in the truck bed.

Despite his road-tested enthusiasm for Romney, there are places that not even Wilson will travel. He skipped Puerto Rico, he admits. (Planes are not his thing.) And he bypassed Alaska. (The logistics, he says, were a nightmare.) “I am a wimp,” he said dryly.

His truck is about to hit the 300,000-mile mark and could use a few repairs. There is an oil leak. Even so, he is gearing up for his longest drive yet, a 38-hour trek from Virginia to California, where Romney will make an appearance on Memorial Day.

He thinks the truck can muddle through until Jan. 20, when he plans to park it, with the Secret Service’s blessing, somewhere on the National Mall in Washington.

“My last event,” he said, “is Romney’s inauguration.”