What to watch: The biggest races in Hawaii are on the Democratic side. Voters in the First Congressional District, centered on Honolulu, will choose from seven candidates to replace Representative Colleen Hanabusa, a Democrat whose campaign for governor has left the seat open. Among the contenders are three state legislators, the lieutenant governor, a member of the Honolulu City Council and former Representative Ed Case. Read more

Senator Mazie K. Hirono, a first-term incumbent who won in 2012 by 26 points, is running unopposed in the Democratic Senate primary. She has long been active in Hawaii politics, having served as a state legislator, lieutenant governor and United States representative.

— LIAM STACK