TOPEKA (AP) — Former Kansas Gov. Bill Graves has endorsed U.S. Sen. Pat Roberts and is recording a statewide radio ad for the three-term Republican incumbent in his tough re-election race.

The Roberts campaign released a letter Wednesday from Graves calling Roberts a tested leader and reasonable problem-solver.

Roberts is in a tight race with independent candidate and Olathe businessman Greg Orman. The challenger is running as a centrist who can break gridlock in Washington.

Graves is a GOP moderate who served as governor from 1995 through 2002 and often clashed with GOP conservatives. He is president of the American Trucking Associations.

Graves’ actions follow Orman’s endorsement by a group of former moderate GOP state legislators.

Roberts campaign manager Corry Bliss said the Graves radio ad should be running by Friday.