Washington (CNN) – Prominent conservative group Club for Growth threw its support Tuesday behind Richard Mourdock in his quest to unseat incumbent Republican Sen. Dick Lugar.
The group's president, Chris Chocola, wrote an opinion piece in National Review Online calling for a "fiscal conservative" to represent Indiana, a mantle he said Lugar cannot claim.
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"Lugar is a good man, and in some ways he has served Indiana and our country well, but his 35-year career in Washington proves that he is no fiscal conservative," Chocola, a former Indiana representative, wrote.
He said a recent vote against a permanent ban on earmarks was the "final straw" for the group.
Lugar, the six-term senator, is locked in a tough primary fight with former Indiana State Treasurer Mourdock.
Fundraising and ads between the two candidates have increased recently ahead of the May GOP primary. Mourdock has attacked Lugar's conservative credentials and support of earmarks while Lugar has attempted to distance himself from President Barack Obama and prove his conservative bona fides.
The Senate stalwart has said he represents the best chance for Republicans to hold onto the Indiana Senate seat in 2012.
In spite of Mourdock's endorsements from conservative and tea party-affiliated organizations, Lugar told CNN's "State of the Union" in December that his record lends itself to support from the grassroots movement.
"I have a very conservative voting record over the course of the time I've served," Lugar told CNN Chief Political Correspondent Candy Crowley. "Certainly unique, I think, in the Senate, of having been a farmer, a small businessman, a Naval officer, a mayor, a school board member. These are grassroots functions that people are dealing with."
Whoever captures the nomination, a Republican is favored to win the seat, according to nonpartisan political handicappers Charlie Cook and Stuart Rothenberg who categorize the race as "likely Republican" and "Republican favored" respectively.