Maine Voters Will Rank Their Top Presidential Candidates in 2020

Maine will soon become the first state to adopt ranked-choice voting in presidential elections.

Gov. Janet Mills, a Democrat, announced on Friday that she would allow a bill recently passed by the Maine Legislature to become law without her signature. The first vote conducted under the new law will be the general election in November 2020.

Under the new system, voters will be able to rank as many candidates as they like in order of preference. The initial count will look only at their first choices, and if one candidate receives a majority, that candidate would win.

If no one receives a majority, however, the candidate with the fewest first-choice votes will be eliminated, and his or her votes will be redistributed to those voters’ second-choice candidates. This process will repeat until one candidate breaks 50 percent.

Proponents say the system ensures that the candidate with the broadest appeal wins. Effectively, it prevents third-party candidates from becoming “spoilers” by siphoning a decisive number of votes from one of the major-party contenders, resulting in a winner that a majority of voters oppose.

In 2016, for instance, votes for the third-party candidates Gary Johnson and Jill Stein exceeded Donald J. Trump’s margin of victory in Florida, Michigan, Pennsylvania and Wisconsin. It is impossible to say whether Mr. Johnson and Ms. Stein decidedly flipped the election because we don’t know who their voters would have picked in a two-way race, but under a ranked system, those voters could have made their second choice clear.

“My experience with ranked-choice voting is that it gives voters a greater voice and it encourages civility among campaigns and candidates at a time when such civility is sorely needed,” Governor Mills wrote in a memo to state legislators on Friday. “At the same time, there are serious questions about the cost and logistics of ranked-choice voting, including collecting and transporting ballots from more than 400 towns in the middle of winter.”

She said that by declining to sign the bill, but letting it become law, she was giving legislators a chance to appropriate more money for the new system. The Portland Press Herald reported that, according to the Maine secretary of state, it would cost about $100,000 to put in place.

Maine voters approved ranked-choice voting for congressional elections in 2016, and it changed the outcome in the state’s Second Congressional District last year. Representative Bruce Poliquin, a Republican, was slightly ahead in the first count, 46.4 percent to 45.5 percent. But once 23,000 ballots cast for independent candidates were redistributed, Mr. Poliquin’s Democratic challenger, Jared Golden, won with 50.5 percent of the vote.

Mr. Poliquin challenged the results in court, arguing that the ranked-choice system was unconstitutional — a view shared by many of Maine’s Republican legislators. (Democrats control both houses of the Maine Legislature.) But a federal judge ruled against Mr. Poliquin, and he did not appeal.