Jim Priest, one of two Democratic candidates to take Markwayne Mullin's seat in the U.S. Senate, sits for an interview in the KOSU studio on July 6. (Photo by Natalie Armour/KOSU)In an Aug. 25 runoff election, Oklahoma voters will choose the Democratic nominee to replace Markwayne Mullin in the U.S. Senate after his March appointment to lead the Department of Homeland Security. In the June primary, N’Kiyla Jasmine Thomas led the five-way Democra…