Sen. Sam Brownback (R-Kan.) will officially announce his retirement Thursday, his office confirmed. Brownback said previously that he would only serve two terms in the Senate and has publicly expressed an interest in running for governor in 2010.

In the wake of Brownback’s announcement, Rep. Jerry Moran (R-Kan.) issued a statement officially tossing his hat into the ring for the Senate seat.

“At the urging of Kansans from all corners of the state, I am now a candidate for the U.S. Senate, with the hope of continuing to be an independent voice for all Kansans,” Moran said. “A formal announcement of my candidacy will come at a later time.”

Rep. Todd Tiahrt (R-Kan.) has put together a steering committee to explore the Senate race as well, setting up a potential primary battle in August 2010 between the two Republican Members.

Gov. Kathleen Sebelius (D), who is term-limited, is the Democrats’ best hope to run for Brownback’s Senate seat. A Democrat has not won a Senate seat in Kansas for more than 70 years.