Updated | 5:41 p.m. BLOOMINGTON, Ind. — Former GOP vice presidential nominee Sarah Palin threw her support behind Treasurer Richard Mourdock’s (R) bid to unseat six-term Sen. Dick Lugar (R-Ind.) today.

It’s a rare endorsement this cycle from the former Alaska governor, who has been notably less aggressive with her Congressional endorsements than in 2010.

“I join commonsense conservatives in endorsing Richard Mourdock to be the next Senator from Indiana,” Palin wrote on her Facebook page. “Richard Mourdock is the conservative choice for Indiana. Senator Lugar’s 36 years of service as a Senator are appreciated, but it’s time for the torch to pass to conservative leadership in Washington that promises to rein in government spending now.”

Palin’s endorsement puts her at odds with her 2008 runningmate, Sen. John McCain (R-Ariz). Lugar’s campaign started airing a radio advertisement this week touting McCain’s support in his own words.

“Indiana is fortunate to have a Senator like Dick Lugar,” McCain says in the radio spot. “Yet, some in Indiana are claiming Dick Lugar is [President Barack] Obama’s friend. That’s ridiculous. And I know it firsthand. Because I fight alongside him every day in the Senate. Dick Lugar is a patriot and a hero, and we need him in the United States Senate.”

Palin’s backing comes less than two weeks before the May 8 primary and after momentum has clearly shifted in Mourdock’s favor. During the last four weeks, national conservative groups, such as the Club for Growth, rallied to Mourdock’s campaign by buying millions in television advertisements on his behalf.

“I appreciate the support of Governor Palin and her endorsement of my campaign to bring conservative values to the U.S. Senate,” Mourdock said in a statement. “Her support will go a long way toward mobilizing conservatives to vote on May 8.”