Conservative Republican Robert Rees announced this afternoon that he is ending the U.S. Senate campaign he launched in January. He explained in a statement posted on his campaign’s website,

Due to the death of Justice Antonin Scalia and the subsequent entrance in to the race by former Lt. Governor Patty Judge, the dynamics of the U.S. Senate race in Iowa have changed.

While we are on pace to get on the ballot, I have decided to not run for U.S. Senate at this time.

Rees had been struggling to collect enough signatures to qualify for the GOP primary ballot. Nominating papers must be submitted to the Iowa Secretary of State’s office by the close of business this Friday, March 18. At this writing, Grassley and two of his four declared Democratic challengers (tate Senator Rob Hogg and former State Senator Tom Fiegen) have qualified to run in the June 7 primary. Former State Representative Bob Krause and Judge have not yet submitted their petitions.

Although Rees was never positioned to defeat Grassley, I regret his exit from the race, because his performance on June 7 would have signaled how many highly engaged Iowa Republicans are dissatisfied with the party’s most popular establishment figure. Little-known Tom Hoefling won just under 17 percent of the vote in his 2014 GOP primary challenge to Governor Terry Branstad.