What to watch: Voters in Oklahoma will cast ballots for the Republican nominee to succeed Gov. Mary Fallin, a two-term incumbent who cannot run for re-election because of term limits. Read more

Ms. Fallin’s approval ratings have suffered as the state has weathered a budget crisis, creating a potentially uphill battle for her lieutenant governor, Todd Lamb, who is angling for the party’s nomination.

Voters will also weigh in on State Question 788, a proposal that would legalize medical marijuana by establishing a marijuana licensing system.

— MAGGIE ASTOR