Sen. Jon Tester’s massive right hand is capable of a vise-grip handshake. In old photographs, however, the Montana wheat-and-barley farmer often has his left hand in the pocket of his barn jacket. Or down by the leg of his jeans.

The three middle fingers on that hand are gone, lost to the blades of a meat grinder when he was 9 years old. The 55-year-old Democrat still uses that hand when fixing the combine at his ranch, flipping through a family album or picking up a burger. The hand does each of those tasks, conspicuously, in his reelection ads.

He says he made no conscious decision to let his injured hand be seen.”The psychology of it all, I don’t know. Maybe I’m more comfortable now in this position,” Tester said last month in his Senate office.

Last fall, the committee that organizes on behalf of Republican Senate candidates created an attack ad featuring a photo of Tester greeting President Barack Obama. The picture showed the senator with his left hand reaching toward the president, and that hand suddenly had all its fingers.

Tester’s campaign spokesman decried “the made-up photo” at the time. But that odd distortion by his opponents might have inadvertently served the senator well. The digital trickery brought more focus to the senator’s childhood accident than the senator might have on his own. The actual hand evokes something indelible about Tester’s life story, about dangerous farm chores, about overcoming adversity.

Candidates use every possible medium and every possible milestone in their lives to boost their prospects when party affiliation isn’t enough — or is potentially lethal. And often their most powerful asset is the most personal anecdote. There are perhaps no better trust-building vehicles than biographical spots. Such ads unspool in heavy rotation during the first half of the election year and prep the electorate for message and attack ads later on. These early commercials use their precious seconds to reinforce a connection to the home state, not the Hill.

“Of course, Jon Tester is not going to talk about his vote for health care or President Obama’s Supreme Court nominees,” said Rob Jesmer, executive director of the National Republican Senatorial Committee, whose photo added the lost fingers to Tester’s hand. “If it’s an election on the issues, he’s gonna lose.” Asked what he thought of the manipulation of the photo, Jesmer would only offer: “I don’t think anything of it.”

While Tester is a Democrat running in a Republican-dominated state, Sen. Scott Brown has the opposite problem in his bid for his reelection. The Massachusetts Republican cloaks himself in red, white and blue as he and his wife sport Red Sox jackets in his campaign ad called “Opening Day.” The baseball-crowd montage takes on nothing more challenging than the adoration of Fenway Park. Another atmospheric ad records the good tidings exchanged during a St. Patrick’s Day parade in Worcester; Brown is clad in a green-and-white striped scarf.

Local color acts as camouflage in other Senate races. “What are elements of the candidate’s personality that are going to work the best? Sometimes it’s using humor, sometimes it’s using emotion,” said Mark Putnam, a strategist who makes ads for Democratic candidates. “And Democrats are maybe a little more daring.”

When Tester was introduced to Montanans as a Senate candidate in 2006, his whimsical commercial about his flattop haircut depicted voters lining up to be similarly shorn. No left hand visible, no mention of the Democratic Party, and the cheerful spot went viral. The mimicry continues in a Democratic Senate primary this year in New Mexico, where a campaign video for Hector Balderas is reprising the theme of tonsorial allegiance. The candidate has a clean-shaven scalp, and a supporter allows a barber to make him “bald for Balderas.”

The biographical ads operate at a different frequency, forming impressions that endure once the political din intensifies. “You don’t want to be the obvious Washington candidate,” said Erik Potholm, a Republican political consultant. “When you’re in an environment that is so hyper-partisan, it’s critical to highlight their personality, their values.”

Also in New Mexico, a leading Republican candidate for Senate, Heather Wilson, skips mention of her five terms in Congress in favor of retelling how she took to the skies as a military pilot, like her father and grandfather before her. A “voice-of-God” narrator transmits the coal-miner background of Tom Smith, the GOP’s challenger to Sen. Robert Casey, D-Pa.

In contrast to these types of prosaic scripts, Heidi Heitkamp leads North Dakotans on a stroll during her political ad called “Places.” Like Tester, she talks to the lens and presents herself as a lone figure on a big-sky landscape. She even wears a barn jacket and stands alongside a truck. Also like Tester, she never says the word Democrat and lets words on a screen, not a script, say “Senate” as her goal.

Her spots are a reintroduction, again, like Tester’s. “Heidi’s personality is a big part of this campaign, in addition to her record as attorney general,” said Putnam, who created her ad campaign. During her 2000 race for governor, she did not let a breast cancer diagnosis end her bid, and she spoke directly to voters in commercials about her mid-campaign mastectomy. She prevailed against the disease but not against her opponent.

“She’s always had a lot of goodwill in the state. People just like her,” said Putnam, who filmed Heitkamp among her sisters, some silos and a sunrise. Whether she’ll recount the story of her breast cancer diagnosis and treatment is an open question.

“That’s something I’d rather not comment on,” her consultant said.

The most poignant of the commercials have the intensity of the “up-close-and-personal” visits with Olympic hopefuls, in which sentiment can trump nationalism. In a political context, identity can eclipse ideology.

“In the age of so much information about candidates that exists on YouTube and elsewhere, we think it’s doubly important” to let the candidate tell his or her story, said Dan Kully, who has done ads for Tester’s two Senate campaigns. “He is so authentic and so unique that we’re having trust in the fact that great candidates make great television.”

Tester said he does nothing for effect, or for the camera. “It’s just this is the way I look: Um, a little bit overweight, and a haircut that’s probably gone out in 1958 and, you know, I’m missing a few fingers and I wear cowboy boots,” the senator said. He has long let his friends razz him about his hand in jest, whether it be his schoolmates back when it happened, or later when he first met Rahm Emanuel, then a member of the U.S. House from Illinois, who lost most of a finger after a on-the-job kitchen accident in his high-school years. “Who I am and where I come from — I think it’s not subliminal in a negative way. It’s just there, okay?” Tester said.

He paused and gestured with both hands. “There are parts of my life that inherently wind up in the frame.”