Dick Leinenkugel (R) is ending his campaign to unseat Sen. Russ Feingold (D-Wis.) less than one month after announcing it.

Leinenkugel, a former brewing company executive, made his surprise announcement Sunday at the Wisconsin Republican Party’s convention. He said he would back businessman Ron Johnson, who began his campaign this month.

In a campaign statement that Wispolitics.com posted online, Leinenkugel said that “spending millions on a divisive primary campaign only serves to give an advantage to Russ Feingold.”

But it would not have been an easy campaign for Leinenkugel, who resigned last month as the Commerce secretary for Wisconsin Gov. Jim Doyle (D).

The campaign of real estate developer Terrence Wall, the other major Republican candidate, released a statement that said Johnson “received the proud endorsement of the architect of Jim Doyle’s failed economy and failed candidate Dick Leinenkugel.”

Businessman Dave Westlake also is seeking the Republican nomination in the Sept. 14 primary.