See Jones v. Dunlap.

“Ranked-choice voting” allows voters to rank three or more candidates in order of preference, rather than choosing just one. If no candidate gets 50% of the vote in the first round of voting, then the lowest-ranked candidates are eliminated, and the votes are counted again. For voters who listed the lowest-ranked candidates as their top choices, their second choices become their first choices in the recount. Supporters of ranked-choice voting say that it ensures that the candidate with the broadest support is elected.

In recent years, Maine implemented ranked-choice voting for elections for president, the U.S. House and the U.S. Senate, and this year it plans to become the first state to use ranked-choice voting in a presidential election. Republicans in Maine wanted to put a referendum on the 2020 ballot to end ranked-choice voting. To do that, they needed to gather signatures totaling at least 10% of the number of votes cast for governor in the last election. But Maine Secretary of State Matthew Dunlap rejected their petition, finding that they fell short of the roughly 63,000 signatures required.

A state trial court disagreed with Dunlap and ruled that the referendum qualified for the ballot. It concluded that the secretary of state could not require the people who circulated the petition to be registered to vote in the place where they were living at the time. The Maine Supreme Judicial Court, the state’s highest court, reversed the lower court’s ruling on Sept. 22. It concluded that the Republicans had not shown that such a requirement violates the First Amendment.

The Republicans went to the U.S. Supreme Court on Oct. 2, asking the justices to block the state from using ranked-choice voting while its appeal is litigated. Justice Stephen Breyer denied the plea on Oct. 6 without comment. That ruling means that the state can go forward with ranked-choice voting and the referendum will not be on the ballot in 2020. Although Maine has only four electoral votes, the presidential election was a tight one in 2016, and if ranked-choice voting had been in effect, it might well have changed the outcome in the state: Hillary Clinton carried the popular vote with 47.83% of ballots cast, Donald Trump was second with 44.87% of the vote, and Libertarian Party candidate Gary Johnson won 5.09% of the vote. This year, the Senate race between Sen. Susan Collins, a Republican, and Sara Gideon, her Democratic challenger, is expected to be a key one in the battle for control of the U.S. Senate.