SHREVEPORT, La. (AP) — The three main contenders in Louisiana’s U.S. Senate race square off Tuesday in a TV debate for the first time, with three weeks to go until Election Day.

Democratic incumbent Mary Landrieu, Republican U.S. Rep. Bill Cassidy and Republican retired Air Force Col. Rob Maness will take questions in Shreveport at Centenary College.

Landrieu and Maness debated last week in New Orleans, but Cassidy refused to attend. His two opponents have repeatedly criticized his unwillingness to agree to more than two TV debates before Nov. 4 in the tight race.

Tuesday’s debate is being held by the Council for A Better Louisiana and Louisiana Public Broadcasting. It will be aired live from 7 p.m. to 8 p.m. on public broadcasting stations.

Landrieu is targeted nationally by Republicans in their effort to retake control of the Senate. Polls show that no candidate is projected to exceed the 50 percent voter support needed to win in Louisiana’s November primary.

The race instead is expected to be decided in a Dec. 6 runoff between Landrieu and Cassidy. Cassidy leads slightly in polls assuming the runoff scenario.

Before the evening debate, both Landrieu and Cassidy had campaign stops highlighting their support for the state’s military installations.

Cassidy was continuing his campaign tour with Republican U.S. Sen. John McCain with a visit to Barksdale Air Force Base near Bossier City. Meanwhile, Landrieu headed to Leesville in central Louisiana to talk about her efforts to preserve jobs and stop a troop reduction at nearby Fort Polk.