What to watch: This will be Maine’s first election using ranked-choice voting, which voters approved in 2016. Under this system, also known as instant-runoff voting, voters rank the candidates in order of preference. If no candidate receives a majority of the first place votes, the last place candidate’s votes are redistributed to his or her voters’ next choices until someone breaks 50 percent. The Associated Press will only call winners for the first round of tabulation. If additional rounds are required to determine a winner, final results will not be available for a few days. Vote counts are from the first round of tabulation. Read more

The twist is that voters will also be voting on whether to continue using ranked-choice voting.

Paul R. LePage, Maine’s controversial Republican governor, cannot run for re-election because of term limits, and Democrats believe they have a good chance of taking his spot. There are seven Democrats in the primary, led by Attorney General Janet Mills and Adam Cote, a lawyer and longtime National Guard member. On the Republican side, there are four candidates, all vying to establish themselves as Mr. LePage’s heir apparent.

— MAGGIE ASTOR