Image credit: Lisa Kunkel/AP

ABC's Elizabeth Hartfield and Kyle Blaine report:

Touting a hard-line economic platform may have been in vogue for many Republican candidates during the 2010 elections, but a new Montana GOP ad for Rep. Denny Rehberg's Senate campaign criticizes one of the signature proposals of his Republican colleagues in the House.

The ad, entitled "Montana First," fashions Rehberg as an "independent thinker" and specifically calls out Rep. Paul Ryan's, R-Wis., budget proposal as harmful to seniors.

"Rehberg refused to support a Republican budget plan that could harm the Medicare programs so many of Montana's seniors rely on," the ad says.

Rehberg was one of only four Republican house members to vote against Ryan's budget plan back in 2011.

Rehberg is in a tight race with incumbent Democratic Sen. Jon Tester. Tester's seat has long been viewed as a potential pick-up by Republicans, who need a net gain of four seats in order to win the majority in the U.S. Senate.

According to David Parker, an associate professor of political science at Montana State University, Rehberg's message against the Ryan plan is an appeal to senior citizens and independents in the state.

"Montana likes people who are independent," Parker said. " There are more independents than any other voting bloc in the state. The state has a political culture that is somewhat suspicious of political parties. "

Parker, who is writing a book about the race to be titled "Battle for the Big Sky," said the intimacy of Montana politics makes the competition much more local than the typical Senate election.

"We call the candidates Jon and Denny here," Parker said. "They're considered family."

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With congressional approval ratings at a dismal low, a great deal of Senate candidates on both sides of the aisle are looking to define themselves as "Washington outsiders" and, to use Rehberg's words, "independent thinkers." In that respect, Rehberg is merely the latest in a trend. However, Rehberg's ad takes it a bit further by calling out his opposition to a specific piece of Republican-sponsored legislation.

The Montana Senate race is expected to be very close. The non-partisan Cook Political Report rates the race as a toss-up.