Richard Fenno, a ground-breaking political scientist at the University of Rochester, studied members of Congress and found that they achieve election –– and re-election –– using three basic tactics: They adopt policies that voters like. They deliver federal money and services. And they persuade voters to trust them, with the fundamental message: I am one of you, or even better, I AM you.

"Politicians believe that a great deal of their support is won by the kind of individual self they present. ... More than most other people, they consciously try to manipulate it," Fenno said in his 1978 book, Home Style: House Members in Their Districts. "Most of the communication ... is not overtly political at all. It is, rather, part of a ceaseless effort to reinforce the underpinnings of trust in the congressman or the congresswoman as a person."

The "I am you, so trust me" message is paramount in Montana, says Dave Parker, a Montana State University political scientist who's hung out with both Rehberg and Tester on the campaign trail. "It's amazing how important identity is in Montana politics," Parker says. In other states, identity politics usually revolve around race, or gender or religion or other demographic traits. In the Interior West, the cowboy image becomes more important, but a candidate can still win in Mormon Utah or urban Colorado and Arizona without riding a horse or a tractor. But in Montana -- the fourth-largest state, with a fraction of the population of metro Phoenix -- "it's about connection to the land," Parker says.

"The Montana identity doesn't consist ONLY of farming, ranching, and hunting," says Luke Conway, a University of Montana associate professor who studies political psychology. "Most of us, while identifying with ranching in some way, do other things for a living." Candidates "just have to find an angle of approach" for reaching voters who have Montana values, Conway says. Republican Judy Martz became governor in 2000 partly by emphasizing her background as a former Olympic skater, rodeo queen and operator of a trash-hauling business. Mainly, candidates have to be perceived as "honest and straightforward ... things a lot of Montanans identify with."

So when Tester attacks Rehberg's rancher-ness, he's questioning the authenticity of Rehberg's identity. Polls consistently show that each candidate has the support of 45 percent to 47 percent of likely voters (for more on Rehberg and Tester policy differences, check the sidebar). Identity politics tend to operate in the margins, outside policy differences, and "for the small percentage of voters that haven't made up their minds yet, this might make the difference," Parker says.

And Tester, who stands in front of a barn in his TV ads, wearing a well-worn Carhartt jacket, has the edge in the identity politics. His trademark $10 flat-top haircut, along with his missing fingers, beam authenticity. His farm is 1,700 dryland acres of lentils and other crops in a completely rural area in central Montana, near a town called Big Sandy, which has only 600 people. His jobs away from the farm, besides his six years in the Senate, have included teaching music in the Big Sandy public school. A New York Times profile right after he won the seat said, "All his life (Tester) has lived no more than two hours from his farm." Tester comes home from Washington, D.C., to do farm chores, plowing fields and changing the clutch on his tractor. That's why Rehberg doesn't attack Tester's farmer credentials directly. Instead, like many Republicans who seek to brand their opponents as "not one of us," Rehberg charges that Tester is a "surrogate" of very un-Montana-style President Barack Obama.

In past Rehberg races, Democrats have tried to take advantage of embarrassing, headline-generating incidents: A spectacular 2009 Flathead Lake crash (Rehberg was a passenger in a speeding motorboat that hit a rocky shore after dark; blood tests revealed that the driver was drunk and that Rehberg had been drinking; a Rehberg aide suffered brain damage and Rehberg had broken bones). A 2004 falling-off-a-horse incident in Kazakhstan (Rehberg had been drinking ceremonial shots of vodka during a political tour, but denied he was drunk). A 1994 remark that could be interpreted as saying, "Let AIDS victims die." (Rehberg insisted he didn't mean it that way, but it landed in Newsweek magazine.) And so on. Opponents say incidents like these show Rehberg's untrustworthiness.

And yet he keeps winning, with a formula that often includes using his family history to make political points. Rehberg usually begins his presentations by noting that he's a "fifth-generation Montana rancher." TV ads show him in a denim shirt, leaning against a ranch fence, or driving a Jeep with a custom license plate: RNCHR MT. He often says that when he stays overnight in D.C., he just sleeps on his office couch -- a rancher camping out in the capital.

Last February, for instance, in a House hearing on a proposal to impose child-labor laws on ranchers, Rehberg began his testimony opposing the regulations with the magic words: "I am a fifth-generation Montana rancher," and then added, "Actually, my great-grandfather was born in Montana in 1873 and left home at 9 (years old) and started breaking horses at Fort Assiniboine in a paid capacity. So you can in fact work as a young man, even back in the 1880s, and survive."

Rehberg describes his great-grandfather as both the source of the family's resilience and the creator of family enterprises that felt the heavy hand of the government. Newspaper stories and government records spanning more than a hundred years, and conversations with several family members, confirm that Albert J. Rehberg -- "A.J." -- was indeed an interesting character, who set the family's course toward prosperity. A.J.'s mother died in childbirth when he was either 4 years old, or 6, or 7 -- A.J. himself told various versions of the story. A.J. "was quite a storyteller -- and he told different stories every time he turned around," recalls one relative who prefers to remain anonymous. Shortly after A.J.'s mother died, he ran away from home -- at age 9 or so -- and began working as a ranch hand. He married a woman from another pioneer family in 1901, and then "the Rehbergs made their home for two years in Henry's Basin, on Box Elder Creek in the north Bearpaw mountains. In 1903, they moved to a site 30 miles below the Old Fort Clagget post office on the Missouri River. ... Each fall the Rehbergs would swim their cattle across the (huge river) and trail them to Big Sandy, for shipment by rail to Chicago," according to a 1963 profile of A.J. in the Billings Gazette.

A.J. Rehberg and his wife, Mary Ada, settled in Billings in 1909, when that city already had more than 10,000 residents. The family put down roots there. A.J. established the Midland Guernsey Dairy Farms on Billings' west side in 1920 and -- by selling milk for less than competitors' prices -- acquired more than 100 cows, pasture and hayfields, processing and delivery operations. He also built an empire of ranchland -- more than 7,000 acres with a log ranch house -- and ran beef cattle. He died in 1963, when Denny was 8, and his descendants took over.

Denny Rehberg sums up the rest of the history -- in speeches and elsewhere, including a YouTube series called Denny's Desk -- like this: The government ruined his family's enterprises, not only through unfair inheritance taxes on the ranchland, but also with intrusive dairy regulations.

In one Denny's Desk video, he says that the Montana Milk Board set prices that prevented his family from selling for less than his competitors. A court battle erupted: "The government came in and messed things up (so) my dad sued them ... and took it all the way to the Montana Supreme Court. He lost the case ... and shut the Midland Guernsey Dairy down," he says. "So dad, when he shut the dairy down, he opened up a restaurant (called the Milky Way). He became a short-order cook ... and for the next 20 years, dad cooked hamburgers and steaks." That experience drew both his father, Jack Rehberg, and himself into politics, he says. In the 1960s, while Jack was a fry cook, he ran for the Legislature as a "small businessman" who was "angry with government," winning two terms in the Montana House and two in the Montana Senate. As Denny watched his father labor to make government less intrusive, he decided to follow in his footsteps, he says.

My research uncovered a somewhat different story: By 1950, Billings was Montana's urban center, with more than 31,000 residents, and its dense neighborhoods were sprawling outward toward the dairy's original 70 acres. "Town was encroaching" on the dairy, recalls Jack Rehberg. Other family members were leaving the dairy business: Denny's grandfather, Wallace S. Rehberg, died in 1954, and Denny's uncle, Wallace A. Rehberg, pursued a career as a university professor out of state. ("He was not meant to be a farmer," Jack Rehberg says.) The family began subdividing the original dairy land in 1953, and shut down the dairy herd no later than the mid-1950s. After that, they ran a milk-bottling company, buying milk from other people's cows and selling it retail at the Milky Way. The decisive court case began in 1961, not with the Rehbergs suing the Milk Control Board, but with the agency suing the Rehbergs because they were refusing to raise their prices to the required minimum, undercutting other retailers who obeyed the law.

When the Montana Supreme Court ruled against the Rehbergs in 1962, it cited a 1934 U.S. Supreme Court ruling that enabled states to set milk prices. The state court pointed to a history of "unfair, unjust, destructive, demoralizing and chaotic conditions and trade practices within the (milk) industry," including excess spoilage, that led to the price regulations. The regulations were heavy-handed and hard on smaller dairies, but some coped with it and kept going in Billings for another 15 or 20 years. Today, although the statewide total has declined precipitously, there are still several hundred dairy farms and 15,000 dairy cows in Montana. "The Milk Board forced us to change our prices, so we decided to get out of it," Jack Rehberg says. "We just plain didn't want to do it anymore -- we had other interests."