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Montana has long prided itself on a refusal to be pigeonholed. It's the kind of place that votes Republican for president but elects Democrats to state office. Politicians wear bolo ties, tout their Montana credentials and use words like "hell" and "crap." People introduce themselves by saying what generation Montanan they are.

Consistently, the state fights against any mandate that smacks of Washington meddling, from the federal speed limit to the Citizens United ruling in early 2010, which opened the door to corporations and unions spending unlimited money on independent ads, echoing an earlier court ruling that equated money with free speech.

Before that, Montana had one of the country's toughest campaign finance laws, dating back 100 years, to the time of the copper kings. After one of those kings bribed state lawmakers to back him as senator, the state banned corporate political spending.

Even after Citizens United, the Montana Supreme Court insisted that Montana's legacy of corruption justified keeping the ban. In June, the U.S. Supreme Court squashed that move, saying the Citizens United decision applied to every state in the nation.

By then, dark money groups were already weighing in on Montana's Senate race.

The TV ads started in March 2011, the month after Rehberg announced. The Environmental Defense Action Fund attacked Rehberg for his stance on mercury emissions. The Electronic Payments Coalition praised Tester for his push to delay implementing new debit-card swipe fees.

"The thing that surprised me a little bit was how early they got involved," said David Parker, an associate professor of political science at Montana State University who tracked all 160 TV commercials as part of a book he is writing on the race. "And I think that was critical, because very early on, they were able to establish the contours of this race. The candidates were just busy putting their organizations together and raising money."

Most of the money spent in 2011 on TV ads came from groups that didn't have to report their donors. They also didn't have to report their ads to the Federal Election Commission, because they didn't specifically tell voters to vote for or against a candidate. Instead of saying "Vote for Rehberg," they said things like "Call Jon Tester. Tell him to stop supporting President Barack Obama." Ads like that only have to be reported to the FEC if they air during the two months before an election.

The only way to compile data on such ad spending is by visiting TV stations, which Parker did. ProPublica helped him collect information on the last round of ads.

Parker's data shows that several heavyweight conservative groups entered the fray in mid-2011 to try to cast Tester, whom they saw as vulnerable, as a big spender.

Crossroads GPS, the dark money group launched by GOP strategist Karl Rove, ran two ads in July 2011 similar to those attacking Democrats in other states for supporting excessive spending.

Also that month, a conservative group called Concerned Women for America Legislative Action Committee ran a sarcastic ad about a new miracle drug called "Spenditol," Washington's answer to America's problems. "Call Sen. Jon Tester," the ad said. "Tell him, stop spending it all." Similar ads ran against Democratic senators up for election in tight races in Florida, Nebraska and Ohio.

Several ads run by conservative groups backfired, messing up in ways that irked Montanans.

The National Republican Senatorial Committee — a party committee that reports its donors — ran an ad that appeared to show Tester with all five digits on his left hand. (Tester is well known for having lost three fingers in a childhood accident involving a meat grinder.) The U.S. Chamber of Commerce misspelled Tester's first name. A Montana cable operator yanked a Crossroads ad for claims the operator deemed false.

"The first one that burned me really bad was from the U.S. Chamber," said Verner Bertelsen, a former Republican state legislator and Montana secretary of state. "I thought — you buggers! We don't need you to come in here and tell us who to vote for."

Starting in July 2011, three new liberal dark money groups ran ads. Patriot Majority USA criticized Republicans for allegedly planning to cut Medicare and help to seniors. The Partnership to Protect Medicare praised Tester for opposing Medicare cuts.

And in October, weeks after forming, the dark money side of Montana Hunters and Anglers, Montana Hunters and Anglers Action!, launched its first TV ad, starring Land Tawney, the group's gap-toothed and camouflage-sporting president, who also served on the Sportsmen's Advisory Panel for Tester. At the time, the super PAC side of the group was basically dormant.

The new Hunters ad accused Rehberg of pushing a bill — House bill 1505 — that supposedly would give Washington politicians control of access to public lands in Montana. Rehberg, one of 60 cosponsors, argued the legislation was necessary to help the Department of Homeland Security protect the state from illegal immigrants, drug smugglers and terrorists.

"Nobody in Montana was talking about that bill," Greenwood said. "I've only heard it talked about in campaign ads. And it played a role throughout the election."