HELENA – Libertarian Rick Breckenridge on Wednesday threw his support behind Republican candidate Matt Rosendale, saying he was standing up against “dark money” in politics.

Breckenridge said he was angry about a recent anonymous campaign mailer that said if Rosendale were elected, it would lead to more government surveillance and that voters should cast votes for Breckenridge instead.

"Matt Rosendale wants to use drones and patrols to spy on our private lives," the mailer reads. "Rick Breckenridge is a true conservative and opposes government intrusion into Montanans' private lives."

GOP officials said there were no names attached to the mailer, which arrived in mailboxes Tuesday, nor was it known how many were sent out. The lack of a name is a violation of state and federal election laws.

Dark money is where the donor is not disclosed and the source of the money is unknown. Rosendale's campaign staff said a complaint with the Federal Election Commission will be filed shortly.

"I am here today to support Matt and his candidacy,” Breckenridge, a surveyor, said during the news conference. “And to endorse him in his continuing effort to be the front man in the cause of liberty.”

Breckenridge said he expected to get 3 percent to 4 percent of the vote in Tuesday’s election, which includes Democratic incumbent Sen. Jon Tester, and that his campaign has spent about $3,000.

“I can’t compete with $50 million Madison Avenue campaign pieces,” he said.

Rosendale thanked Breckenridge.

"I am honored to have endorsement of Rick Breckenridge," he said. "I really appreciate him in joining me in (condemning) a dark money mailer that" he said was distributed by allies of Tester.

Tester's campaign disavowed the mailer.

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"This is yet another lie from Matt Rosendale - our campaign had nothing to do with this mailer, and Jon believes all campaign expenditures should be disclosed," Tester spokesman Chris Meagher said. "We condemn this mailer and any other efforts like it. Period. It’s ironic Matt Rosendale is now up in arms about a mailer with no disclosure, since he voted against a bipartisan measure requiring a disclaimer on election materials like direct mail funded by anonymous sources. Unfortunately, Jon Tester is the only candidate in this race fighting to get dark money out of our elections.”

Earlier in the day it was believed Breckenridge had pulled from the race. Breckenridge said later he remains on the ballot and is a candidate, but does support Rosendale.

Francis Wendt, chair of the Montana Libertarian Party, said his party was not endorsing Rosendale.

"We do not endorse any candidate in the Democratic or Republican party," he said, adding most Libertarians are pragmatist and know their chances of winning are often slim.

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Breckenridge said he discussed his decision with fellow Libertarians the night before.

"This was not a party decision but my decision alone," he said.

He said the flier went to friends, neighbors and business associates with no disclaimer and "looked like it came from me."

Tester, who is seeking a third term, and Rosendale are locked in a tight race that is too close to call. President Donald J. Trump has made three visits to Montana to campaign for Rosendale and GOP Rep. Greg Gianforte. with a fourth visit planned for Saturday in Bozeman.

David Parker, an associate professor of political science at Montana State University, said a large amount of absentee ballots are in the mail or returned and he doubted Breckenridge's decision would have much impact on Tuesday's election.

Breckenridge's participation has threatened to take away votes that might otherwise go toward the Republican and boost Tester's chances next week.

"We already have 242,000 votes in…. and Rick Breckenridge is polling only around 2 percent," he said. "You’d have to assume all those votes will still show up and go to Matt if the polling is accurate. And I think that’s simply unlikely."

He said the "low level of support that Breckenridge is getting is probably hard core Libertarian support that will likely simply vote Libertarian no matter what."

Reached after the news conference, Breckenridge told the Tribune he was a “realist” about his chances of winning and what pulling from the race meant.

“This isn’t the Alamo, this isn’t Custer’s Last Stand. I will live to fight another day,” he said. “I am a victim in this dark money campaign and as a victim you sometimes have to expose yourself to an uncomfortable reality.”

Breckenridge said his decision would likely impact about 1 percent of the vote and noted most people have probably voted already by absentee ballot.

"I am making a stand above and beyond my personal desires," he said.

The mailer is reminiscent of tactics used by Democratic-friendly groups in Tester's 2012 race to promote Libertarian candidate Dan Cox and siphon Republican voters from Rep. Denny Rehberg.

The Associated Press contributed to this story. Reach Phil Drake at 406-422-0772 or pdrake@greatfallstribune.com.