Milton Wolf, a conservative primary challenger to Sen. Pat RobertsCharles (Pat) Patrick RobertsGOP senators introduce resolution endorsing ICE Senate passes mammoth farm bill Moderates need to hold firm against radical right on Farm Bill MORE (R-Kan.), picked up the endorsement of a prominent national conservative group on Tuesday.

Senate Conservatives Fund Executive Director Matt Hoskins called Wolf a "principled conservative" in the group's endorsement.

"He's not a career politician. He's a doctor who understands exactly why Obamacare must be repealed," Hoskins said. "Kansas Republicans deserve a real choice this election, and Dr. Wolf gives them a chance to send someone new to Washington who will shake things up and bring about real change."

Wolf is Obama's second cousin once removed.

Roberts, who was first elected to the Senate in 1996, won his last election with 60 percent of the vote.

He's a staunch conservative and isn't typically considered vulnerable to conservative attacks, but Wolf has long criticized the incumbent, accusing him of raising the debt ceiling and supporting the Wall Street bailout.

The Senate Conservatives Fund has also endorsed conservative primary candidates in Senate races in Mississippi, Kentucky, Nebraska and Louisiana.