Indiana Treasurer Richard Mourdock officially kicked off his campaign Tuesday to challenge long-time Sen. Dick Lugar in 2012, calling the veteran senator "Barack Obama's favorite Republican."Mourdock, a favorite of the tea party, plans a conservative challenge to Lugar, who some Republicans believe isn't conservative enough. Analysis: Capitol WatchBlog: Will Democrats Decide? "I'm not here to bash Lugar. I used to vote for him, but not anymore.... He's supported that agenda time and time again. He's known for bipartisanship," Mourdock said at the announcement. "In fact some, say he has earned the title as President Obama's favorite Republican senator. My friends, that is a title I will never hold."Lugar has held the senate seat for 35 years after being first elected in 1976. He was also previously mayor of Indianapolis. Mourdock was re-elected as state treasurer in November.In a news release that accompanied Mourdock's announcement to about 150 supporters, the candidate ripped Lugar for voting for supporting Sonia Sotomayor and Elena Kagan, Obama's Supreme Court nominees, and for co-sponsoring the DREAM Act, an immigration amnesty proposal.Mourdock, 60, said he believes Lugar has lost touch with his Indiana constituents and is not upholding conservative ideals. He also circulated a list, claiming 67 of 92 county Republican Party chairmen support his candidacy.Howard County Republican Chairman Craig Dunn put his support behind Mourdock in November, saying he can't stomach Lugar's recent record."Votes Elena Kagan, Sotomayor, the DREAM Act, START (Strategic Arms Reduction) treaty, failure to restrict earmarks. He is totally out of step with the movement in the Republican Party," Dunn said.Lugar is attending an energy security conference in Puerto Rico, but his spokesman defended his conservative record."He's voted against the stimulus. He voted against the president's budget, several of his spending bills. He voted against Cash for Clunkers. He voted against the health care bill," said spokesman Mark Hayes. "The majority of the president's domestic initiatives, Senator Lugar has opposed those."Lugar has raised $2.5 million in campaign funds.When asked who Gov. Mitch Daniels would be voting for next year, a representative with his office said the governor would be voting for Lugar.