Topeka ? U.S. Sen. Sam Brownback, R-Kan., and Kansas Secretary of State Ron Thornburgh, who briefly were political rivals, will make a joint announcement on Thursday.

Brownback, considered a conservative Republican, is running for the GOP nomination for governor in 2010. Thornburgh, who has been considered a moderate Republican, had also been a primary candidate, but dropped out in June because of a lack of funding. At the time, he declined to make an endorsement, and said that he would not seek re-election to his current job.

No other Republican has surfaced to challenge Brownback in the August primary. And there has been some speculation that Brownback will select a lieutenant governor running mate early.

Kansas Republican Party Chairwoman Amanda Adkins will be on hand at the joint announcement, which will be made at state GOP headquarters.