The national group "Senate Conservatives Fund" has endorsed Milton Wolf in campaign against Senator Roberts for the Kansas Republican primary.
Wolf is a radiologist in Leawood, Kansas, and is running against Roberts as a tea party candidate.
He's criticized Roberts on budget, tax and health care issues and sees the endorsement as helping him build momentum.
Former South Carolina Senator Jim DeMint founded the Senate Conservatives Fund.
U.S. Sen. Pat Roberts may have a primary challenge in his bid for re-election.
Milton Wolf is inviting supporters on his website to a "major announcement" Tuesday night regarding the 2014 Kansas Senate campaign.
The Johnson County doctor is expected to say he's moving ahead with a Republican primary challenge to Roberts.
Roberts is seeking a fourth six-year term in the U.S. Senate. No Democrat has announced plans to run.