INDIANAPOLIS (AP) — Democratic former Sen. Evan Bayh and Republican Rep. Todd Young are set to face each other in what could be their only debate during their bitter campaign for Indiana’s open U.S. Senate seat.

They will be joined by Libertarian candidate Lucy Brenton for the hourlong debate beginning at 7 p.m. EDT Tuesday. The nonprofit Indiana Debate Commission says it will be broadcast by several television and radio stations.

The campaign to replace retiring Republican Sen. Dan Coats has become a key one as the GOP looks to retain its narrow Senate majority.

National Republican groups have spent millions on TV commercials attacking Bayh’s work in Washington, D.C., since leaving the Senate in 2010. Bayh is criticizing Young for opposing the 2008 auto bailout that rescued General Motors and Chrysler.