OKLAHOMA CITY (AP) — With the announcement earlier this year that longtime Republican U.S. Sen. Jim Inhofe plans to step down from office early, Oklahoma voters have the rare opportunity to cast ballots on Tuesday for candidates for both of the state's U.S. Senate seats, although Republicans will be heavily favored to retain both seats in the fall.

Republican U.S. Sen. James Lankford, 54, is running for reelection to a full six-year term and is facing a feisty GOP primary challenger in Tulsa pastor Jackson Lahmeyer, 30, a political newcomer who has accused Lankford of not being conservative en...