Republicans worry that if Kris Kobach, a polarizing figure in the state, wins the nomination, it would pave the way for Democrats to capture the seat and perhaps gain control of the Senate.
Some in the G.O.P. want President Trump to endorse the opponent of Kris Kobach, who they worry could cost them a traditionally safe Senate seat. So far, the White House has declined to do so.
Mr. Kobach’s polarizing presence in a race in a reliably Republican stronghold has party leaders worried that Kansas will become a high-stakes battleground for control of the Senate.
In contests in Kentucky, South Carolina, Kansas, Maine, Colorado and Arizona, Democratic candidates raised more money in the first quarter of 2020 than their Republican opponents.