(CNN) Senate Republicans are openly agonizing about the possibility Don Blankenship will win the GOP primary for a US Senate seat in West Virginia on Tuesday and set up a general election against Sen. Joe Manchin that the Democratic incumbent might win.

"Let's hope and pray that doesn't happen," said Sen. John Thune of South Dakota, the third-ranking GOP leader.

GOP concerns about the contentious candidate winning are so great they were discussed Monday at a private meeting of top Republican leaders in Majority Leader Mitch McConnell's Capitol office, Thune said.

"We are starting to think through the various scenarios," Thune said. "It would not be good."

An administration official said the White House is becoming concerned that Blankenship could become "Roy Moore on steroids" if he wins the primary. The official said there is a worry that the other candidates in the race will split the establishment vote, giving Blankenship the opportunity to capture the nomination.

Read More