TOPEKA, Kan. (AP) — Republican Sen. Pat Roberts is trying to bolster his support among GOP and unaffiliated voters in Kansas with a recorded telephone message from former GOP presidential candidate Mitt Romney.

Roberts’ campaign said the call with Romney’s endorsement was going to 400,000 voters across the state Wednesday.

Roberts is in a tougher-than-expected race for re-election against independent candidate Greg Orman.

Orman is running as a centrist, and his campaign says voters are tired of gridlock in Washington.

Romney was the 2012 Republican nominee against Democratic President Barack Obama.

In the message, Romney calls Roberts a trusted conservative. Romney says Roberts is needed in Washington to block the agenda of Obama and Democrat Senate Majority Leader Harry Reid.

Orman has said voters are interested in solving the nation’s problems, not partisanship.