LAWRENCE, Kan. (AP) — Sen. Pat Roberts is airing a television advertisement in his re-election campaign in which he vows to filibuster any federal effort to house terrorism detainees at Fort Leavenworth that are now being held in Guantanamo Bay, Cuba.

Roberts made the statement earlier this month while campaigning for re-election. He’s seeking a fourth term in a surprisingly competitive race with independent candidate Greg Orman, a Kansas City-area businessman.

President Barack Obama this month was weighing bringing detainees to U.S. federal prisons, such as Leavenworth.

Roberts has tried to paint Orman as a Democrat and automatic vote for Obama’s agenda, though Orman repeated Tuesday that he opposes bringing detainees to U.S. prisons.

Senate Republicans need to gain six seats to capture a majority and weren’t counting on having to defend GOP-heavy Kansas.