"Building houses and mansion ranching is not ranching," Tester said at their first debate this summer.
The razor-tight race may come down to who is "more Montana."
Rehberg's campaign acknowledges that Tester may spend more of his free time farming, but the challenger says the first-term Democrat's support for President Barack Obama's mandate that most everyone buy health insurance runs counter to Montanans' libertarian streak.
Rehberg cites his long roots in ranching prior to leasing out his land due to the demands of his congressional office. He says managing cows is different from farming and requires a full-time presence.
"Frankly I am sorry for the people of Montana that he is wasting so much time as a U.S. senator talking about what a great farmer he is," Rehberg said in an interview. "Maybe he ought to spend a little bit more time trying to help get people back to work and expand the economy because that is what I am focused on. I don't think the people of Montana would particularly want me sitting around the ranch trying to keep the cows in the fence and putting water in front of them and such."
Each candidate lays claim and blame over who's the least elite, most authentic and best able to represent the state's 1 million rural residents in Washington, a city they view with great distrust. Tester's two predecessors lost their populist appeal and re-election bids after becoming too identified with the city's Beltway interests.
Tester's victory in 2006 helped Senate Democrats take over from Republicans. He won in a squeaker after arguing that three terms in Washington had corrupted incumbent Republican Sen. Conrad Burns, who was embroiled in the Jack Abramoff influence-peddling scandal. It helped that Tester, who has a flattop haircut and is missing a few fingers because of a butchering accident, looks every bit the dryland grain farmer he is, rumpled off-the-rack Sears suits and all.
Now that Tester is the incumbent, he's having to defend himself from attacks that he sold out to banks on debit card swipe fees and, perhaps more harmful, that he is a rubber stamp for Obama administration policies unpopular in Montana.
He is trying to distance himself from Obama by pointing out his opposition to new environmental regulations and proposed farm child labor rules that were considered but abandoned by the Labor Department. Tester also is pushing for the Keystone XL oil pipeline that runs from the Canadian oil fields south through Montana. Obama has postponed a decision on it until after the election.
But Tester wouldn't take back the politically harmful health care vote if he could do the first term over gain. Instead he said he wishes he had done more to stop the intervention in Afghanistan and bring the troops home, pointing to the maimed soldiers he's visited and the billions spent on the war.
Rehberg said he would take back the vote for the Bush administration's post-Sept. 11 program to secure driver's licenses. The Real ID act was intended to help thwart terrorists, but the congressman said that at the time of the vote, he did not know that many in his state would come to despite the program.
Montana State University political scientist David Parker says Republicans "are attacking Tester in ways that would push him away from that image as a Montana farmer: One, he is with Obama. Two, he is a nasty guy. And three, yeah, he makes and eats his own beef, but he votes against Montanans and their interests."
Parker said that Tester's connection to the land is his strongest asset, and he can't have Rehberg seen as a rancher, too, because that would obscure the differences between them.
The Tester campaign argues that Rehberg hasn't bought or sold cattle since at least 2000, citing state livestock inspection records. Some of the attacks deride Rehberg as a multimillionaire land developer.
While Rehberg is the challenger in the race, he has been in statewide politics much longer than Tester and is just as well-known. He was an ardent supporter of conservatives polices as a state legislator in the 1980s. He became lieutenant governor in 1991 and in 1996 he almost defeated veteran Democratic Sen. Max Baucus.
Rehberg isn't ceding the ranching background. He often talks about his family being forced to sell parts of the historic family ranch near Billings in order to pay inheritance taxes the derided federal "death tax" after his grandmother died in the 1970s. He managed the family ranch for several years before winning the state's lone U.S. House seat in 2000.
In the House, Rehberg carefully has maintained his conservative credentials even while sometimes turning on Republicans, such as when he backed the 2009 expansion of the Children's Health Insurance Program. Last year, he was one of just three other Republicans in the House to oppose Rep. Paul Ryan's budget proposal that would transform Medicare.
Rehberg holds an advantage in the more rural parts of the state, and even expects to carry Chouteau County that is home to Tester's Big Sandy farm and about 6,000 people. Those voters largely went for Burns in 2006.
Tester reminds voters why they picked him in the first place. He was first a music teacher and a farmer, then a state legislator and farmer. If he loses the election, he said he will happily return to just farming.
He spent free time in late July and early August harvesting his crops or at least those that survived what Tester called one of the worst hail storms to his farm in 35 years. "I take my vacation on the combine and tractor. I am not bitchin' either, I like it that way," he told The Associated Press in an interview.
Important race for Senate control
The Rehberg-Tester race, one of a few that will determine which party controls the Senate in 2013, is drawing millions of dollars in political money from out-of-state interest groups. Republicans need a net gain of four seats three if GOP candidate Mitt Romney wins the presidency, because his vice president could break a tie vote to regain control. Missouri, Montana, Nebraska, North Dakota, Virginia and Wisconsin represent their best chances for pickups.