Sen. Pat RobertsCharles (Pat) Patrick RobertsRepublicans think Trump is losing trade war Senate GOP urges Trump administration to work closely with Congress on NAFTA This week: House GOP regroups after farm bill failure MORE (R-Kan.) has avoided a second conservative challenger entering his primary, leaving him to battle radiologist Milton Wolf for reelection in August. 

As The Hill first reported last month, Kansas state Sen. Dennis Pyle had floated the possibility of running against Roberts, going so far as to launch an exploratory committee. He said he had been considering it because conservatives have told him “they feel that Mr. Wolf’s challenge is going to fall significantly short.”

But Kansas’s filing deadline closed on Monday without Pyle jumping in the race. Wolf has already picked up a handful of national conservative endorsements, and Pyle said that, while he thought he would’ve had a better chance against Roberts, he didn’t want to divide the conservative vote.

"I choose now to do what Mr. Wolf will not do by putting the cause first," Pyle said in a statement.

Roberts, who was first elected to the Senate in 1996, won his last election with 60 percent of the vote and isn't typically considered vulnerable to conservative attacks. He's drawn scrutiny, however, over reports that he no longer owns a home in Kansas and stays with donors when he goes back to visit, which Wolf says is an indication of how out of touch he is with the state.

But Wolf was damaged in recent months by reports revealing he mocked his patients’ X-rays in Facebook posts, and no survey of the race has yet shown him picking up any traction.