Jon Tester, United States senator, is face down in the mud. Earlier today, Tester and his wife, Sharla, drove from Great Falls, Mont., to their home, T-Bone Farms, 80 miles northeast. It’s a journey the Testers have been making nearly every weekend since Jon joined the Senate in January 2007. As usual, they followed the Teton River through sloping sandstone canyons and out onto a vast expanse of flat, treeless farmland, with only the occasional man-made interruption: the United Grain silos in Kershaw, the Ace High Casino in Loma, a billboard about chewing tobacco. “Quitting Was Tough,” it said, “But I’m Tougher.” The trip took 80 minutes.

Not everyone, however, enjoyed such a pleasant drive. After turning down Son Lane, the long, muddy path that leads to Tester’s 1,800-acre farm, the senator’s press secretary, Aaron Murphy, got stuck in the muck. Now Tester—and his red Case tractor—are trying to pull him out. Tester loops a set of chains around the Ford Fusion’s rear wheels. He tells Murphy to put it in neutral and straighten out. He climbs into the cab, reverses the rig, and drags his staffer’s car backward out of the mud. But when Tester bends down to remove the chains, he can’t quite get them loose. First he’s hunched over, tugging. Then he’s on his knees. “Damn things,” he says. Finally, Tester lowers himself onto his ample belly—he’s about 6 foot 1, nearly 300 pounds, with a Roger Maris flattop and a left hand that’s missing its three middle fingers, which were severed by a meat grinder when he was 9—and squints into the chassis. Seconds later, he frees the stubborn links. “Got ’em,” he says, standing back up. He doesn’t bother to brush the mud from his chest.

Tester is not the most powerful senator in Washington, and he’s far from the most polished. But because his rural constituency will help determine who controls Congress, and perhaps even the presidency, after 2012, he’s about to become one of the most important. When Rep. Denny Rehberg, Montana’s best-known Republican, launched his own Senate bid in February, Tester’s chances for reelection plummeted. He’s only the tip of the rural iceberg. According to Charlie Cook, the Capitol Hill handicapper, nine Senate races now qualify as “tossups.” Four will test the staying power of Democratic incumbents: Ben Nelson in Nebraska, Claire McCaskill in Missouri, Joe Manchin in West Virginia, and Tester. Three will take place in states where Democrats are retiring: Virginia, New Mexico, and North Dakota. And all seven of these contests will largely be decided by people more like Jon Tester than Chuck Schumer. The math is simple: if Democrats can’t connect with small-town voters, they will lose the Senate next November—and make it difficult for President Obama, who held his own among rural Americans in 2008, to recapture states like North Carolina that put him over the top last time around.

But Tester, who was elected with strong support from the netroots, is in a special bind. By doing what he says he was sent to Washington to do—represent his rural constituents—Montana’s junior senator is beginning to irk the activists and fundraisers who propelled him to victory in the first place. In December, Tester voted against the DREAM Act, which would’ve created a pathway to citizenship for the foreign-born children of illegal immigrants. His strategists insist that a yea vote would have sunk the senator in anti-“amnesty” Montana, but Markos Moulitsas of Daily Kos, whose followers filled Tester’s coffers with $343,000 in 2006, was furious anyway. “He is … the Democrat I will most be happy to see go down in defeat,” Moulitsas wrote. “And he will.” Tester was undeterred. As they hammered out April’s shutdown-averting budget, legislators stripped every environmental add-on from the package except one: a plan to end federal protections and allow hunting of the region’s gray wolves, which prey on livestock and game. The rider was Congress’s first-ever attempt to remove an animal from the endangered-species list, and it angered activists, with one, Michael Garrity, going so far as to compare “local control” of wolves to “turning over the civil rights problem in the ’60s to the governors of Mississippi and Alabama.” Turns out it was Tester’s handiwork. “I’m tired of the triangulation,” says Paul Edwards, a Montana environmentalist (and part-time Los Angeleno) who raised $50,000 for Tester in 2006. “You know, ‘He’s the best we’ve got. The others would be too terrible.’ Well, let ’em be terrible. Better the enemy I know than the enemy I thought was my friend.”

When Tester arrived on Capitol Hill, coastal types were quick to call him a New Kind of Democrat, which had a nice ring to it. Unfortunately, they couldn’t agree on what kind of Democrat he was. Some pundits pegged him as a populist. Others saw him as a Western libertarian. One even floated the phrase “macho Dem.” But as his recent decisions have demonstrated, Tester is, at root, something rarer and riskier than all that: a rural politician in an overwhelmingly urban party. “My stances are shaped by where I come from,” he told me in March. “Folks out here face challenges that most people don’t realize.” And so the question that will define the next 18 months, for Tester and his party, is not only whether there’s room in rural America for Democrats; it’s whether there’s room in the Democratic Party for rural Americans.

Tester comes by his backcountry persona honestly. He was born in the small, remote town of Havre, 35 miles south of Saskatchewan. His mother’s parents were Swedish homesteaders who established the family farm in 1912; his father’s family were Mormons who followed Brigham Young to Salt Lake City, where many of his relatives still live and practice the religion. When a Republican neighbor quit the state Senate in 1997, Tester made the leap into politics—a dream he’d nurtured “since visiting the legislature in high school.” Over two terms, he rose from freshman to whip to minority leader to president. But the Montana Senate meets for only 90 days every two years, meaning that by the time Tester decided to challenge Republican Sen. Conrad Burns, the sum total of his legislative experience was 12 months in Helena.

Even now, after four years in Washington, D.C., Tester can still seem rather unsenatorial. Within minutes of meeting me, over a 6 a.m. breakfast of danishes, muffins, and pointlessly fat-free milk, he openly referred to one local environmentalist as a “wahoo.” The next day, I heard him characterizing another liberal activist as “numbnuts.” Tester uses the word “cool” as often as a tween, and I lost count of all the loogies he hocked in my presence. While waiting to be interviewed on KTVQ, he proposed a novel solution to April’s budget impasse: locking lawmakers in a closet, “two by two,” until they reach an agreement. “Give ’em a baseball bat,” he said. “The guy who wins gets whatever he wants. Or gal! I mean, Barbara Mikulski”—the squat, 74-year-old senior senator from Maryland—“could kick the shit out of all of them.” Most senators have an earthy side, but they tend to tone it down when a reporter is in the room. Tester turns it up.

The senator and his staff are eager to emphasize the stylistic contrasts with Rehberg, a real-estate developer and cashmere-goat rancher worth tens of millions. But substance will decide the 2012 race, not style. Traveling with Tester—from a dental facility in Billings to a firehouse in Miles City, from a sportsmen’s meeting in Great Falls to the farm in Big Sandy—it’s clear that being a rural Democrat in the age of Obama is much trickier than just acting like one.

Consider the gray wolf. Washington’s original recovery goal for the species was 300. That milestone was passed more than a decade ago; today the regional population exceeds 1,600. The desire to wrest control of wolves from D.C. is a classic states’-rights issue, spiked with Western machismo, and during my time with Tester it was the only topic that came up everywhere he went: hotels, coffee shops, art auctions. “What do you think about wolves?” a sixth grader asked during an assembly in Miles City. “I think we should start hunting them again!” Tester said. The kids let out their loudest cheer of the afternoon. After the event, I asked Tester about the rural-urban divide. “Maybe we should release some wolves in New York City,” he said. “You know, to clarify things.”

Logging is a similar story. Recently, Tester has tried to revive a stalled bill that was intended as a compromise between the timber community and conservationists: 700,000 acres of new wilderness in exchange for light-on-the-land logging projects designed to create jobs in the flagging industry. But liberal environmentalists, both in state and out, have decided that the measure is “wacky” and “cedes control of national forests to local timber mills,” says Missoula Independent columnist George Ochenski. “It’s not winning [Tester] admirers on his side.”

The dizziest debate, however, may be debit cards. Buried in last year’s financial-reform bill was an amendment designed to cap the swipe fees that banks charge merchants for debit-card sales. It was precisely the kind of “populist” measure that Tester’s netroots fans would expect him to support, which is why bloggers lost it when Tester pitched a two-year delay in March. (“Wall Street buying our politicians,” one fumed.) And yet the senator says he’s looking out for Montana, not Citibank. As he told the Billings Chamber of Commerce over lunch, “The big guys will be fine if we cap these fees. It’s Montana’s credit unions and community banks that will suffer.” The crowd, a mixture of bankers and accountants, nodded in agreement.

When liberals warn of rapacious hunters, loggers, and financiers, they have a point. But the left’s knee-jerk reaction—to assume that Tester is a sellout instead of a Democrat struggling to represent a rural constituency—ignores the very real differences between Big Sandy and the Big Apple and reveals how unrural the party’s default setting really is. In 2006, Tester defeated Burns by a mere 3,500 votes, and with Democratic support down from its 2006-08 peak, he’ll need all the momentum he can muster. If the left decides Tester is indistinguishable from a Republican, he may be in trouble. That’s particularly true when Rehberg’s plan is to convince independents that Tester, who has voted with his party 93 percent of the time, is indistinguishable from Obama, whose Montana approval rating is 39 percent—and whom Tester himself is reluctant to compliment or invite out on the trail.

With his aide safely out of the mud, Tester heads to the garage—NAPA air compressors, orphaned car seats, empty barrels of Utz Cheese Balls—to grease up his Brandt Grain Vac, which, he brags, “can fill my semi in 20 minutes.” It’s strange to hear a senator talk about his semi, but Tester’s not alone. In other states, other rural Democrats are facing the same challenge as Tester, or will be soon: a new, wired landscape that lets them draw support from every corner of the country but holds them to a one-size-fits-all standard of urban liberalism in return. It’s Tip O’Neill’s famous axiom in reverse: now all politics is national. Tester, for one, is aware that he’s a throwback, with all the related risks and rewards. “When I’m spending 16 hours on a tractor, it gives me some opportunity to sort through issues in solitude,” he tells me. “That’s the way the old-timers did it, the Washingtons and the Jeffersons.” He pauses and glances out the window, across the winter wheat fields. “But it’s a different world now.”