BOISE - Idaho voters will narrow the candidates in each primary race Tuesday after being subjected to lengthy and expensive campaigning efforts that have taken a negative turn.

The GOP primary is often considered the most competitive leg of the election season because Republican candidates rarely face a strong Democratic challenge in November.

The top races are the open seats for governor and the 1st Congressional District. Idaho's lieutenant governor and state treasurer seats are also up for grabs without an incumbent.

VOTER GUIDE: May 2018 Primary

Voter turnout in Idaho has hovered around 25 percent among registered voters in recent primary election cycles.

Idahoans can register to vote the day of elections. However, only registered Republicans can participate in Idaho's GOP primary.