Maine is set to become the first state to allow voters to rank candidates in a general presidential election.

Democratic Gov. Janet Mills said Friday she'll allow such a bill to become law in January without her signature.

The legislation requires ranked-choice voting in presidential elections and primaries.

Mills' office says ranked voting won't be used in a planned presidential primary in March 2020. But future presidential primaries would use it.

Under the system, voters rank three or more candidates on a ballot in order of preference. If no candidate gets more than 50%, the last-place candidate is eliminated.

The second-choice votes of everyone who ranked that candidate first are allocated until someone receives over 50%.

Mills says ranking could empower voters. But she expresses fiscal and logistical concerns.