To win a primary race in Maine next month, candidates will have to do something unusual: Aim not just to be voters' first choice, but their second, third and perhaps fourth choice, too.

Maine is the first state to use the ranked-choice voting system for statewide and federal elections, earning plaudits from advocates who say it is a step toward making the U.S. a better, less polarized democracy.

How it works: In primaries with more than two candidates, voters will rank candidates in order of preference on their ballots. If no candidate receives a majority of first-choice votes, the candidate with the fewest number of first-choice votes is eliminated. Ballots cast for the eliminated candidate are then recast for the voter's second-choice pick. The elimination and retabulation process continues until there are two candidates left in the race; the one with the most votes is declared the winner.

(While the winning candidate may well reach the majority threshold earlier in the counting process, Maine law requires the elimination and retabulation cycle to continue until the field is narrowed to two, giving the winner the largest possible majority.)

"It gives voters more choice, more voice," said Kyle Bailey, the campaign manager for the Committee for Ranked Choice Voting, a group that has lead the three-year fight to implement the system in Maine.

Bailey said the system discourages scorched-earth politics and fringe candidates who appeal exclusively to a narrow part of the electorate and forces candidates to build a coalition of support — because they may need voters to consider ranking them as their second or third choices.

Critics, however, say the old system worked fine and protest spending money to put a new one in place. Maine Republicans, in particular, have chafed under the court-mandated implementation of ranked-choice voting, and argue they should have the power to decide the rules of their primaries.