TOPEKA, Kan. (AP) — An arcane legal dispute over the lack of a Democratic candidate for the U.S. Senate in Kansas could upend a key contest in the fight for control of the Senate.

The national spotlight is on three-term Republican Sen. Pat Roberts and independent challenger Greg Orman.

But a case being heard Monday by a three-judge panel in Shawnee County District Court centers on whether state law requires Democrats to pick a new candidate after Chad Taylor withdrew earlier this month.

Some Democrats pushed Taylor out. They viewed Orman as a stronger rival for Roberts and wanted to avoid a split in the anti-Roberts vote.

Republicans need to gain six seats for a Senate majority and have counted on Roberts winning.

The judges are expected to rule this week.