On Tuesday, Maine became the first state to conduct a federal general election using ranked-choice voting, a system proponents say can reduce polarization and break the two-party stranglehold on American politics.

Sen. Angus King, the independent incumbent, became the first U.S. senator elected by ranked-choice voting; Rep. Chellie Pingree, a Democrat incumbent who represents the Maine coast around Portland, was easily re-elected.* The ballots looked like this.

Under ranked-choice voting, voters are free to vote for the candidate they like most, without worrying about a spoiler effect. The candidate with the fewest first-place votes is eliminated, and those votes are redistributed to the remaining candidates. The process continues until all votes have been assigned to two candidates. It has been used in U.S. mayoral elections, most recently in San Francisco this summer, but never at a state or federal level.

The new system may wind up determining control in Maine’s 2nd District, which makes up the rest of the state. Democrat Jared Golden challenged incumbent Rep. Bruce Poliquin, the last Republican congressman in New England, in a race that also featured two independent candidates. By early Wednesday, with many votes left to count, the major-party candidates were neck and neck, with a pair of independent candidates keeping everything from crossing 50 percent.

In another state, that might have meant a squeaker of a victory for one candidate and several thousand “wasted” votes. But it didn’t, because this is Maine, and all those third-party voters will have their votes redistributed to one of the leading candidates based on their preferences. The race is likely to be settled on Wednesday.

There are some potential downsides to ranked-choice voting, as Evelyn Lamb wrote in Slate in 2016:

As a simplistic example, say 25 percent of voters had the preference rank ABC, 35 percent voted BCA, and 40 percent voted CAB. Candidate A got the fewest first-place votes, so we take A away entirely. Now 60 percent of people have the preference order BC over 40 percent for CB, so B wins. This is frustrating because more people ranked candidate C as their first choice than any other first choice. And going back to the original rankings shows that if C wasn’t going to win, more people would have preferred A to B. But the runoff system sticks us with candidate B.

But that situation—in which the electorate is more or less evenly divided in three totally different preference arrangements—is pretty improbable. Instead, the system will likely encourage candidates to run third-party campaigns, and voters to support them. In primaries, it will make moderates with wider, weaker support likely to prevail over extreme candidates with fewer but more dedicated supporters.

Maine voters elected to use ranked-choice voting in 2016, partly as a reaction to a two-decade period in which no governor won a majority, due to strong third-party showings. But last year, the state Supreme Court struck down the provision for use in state-level elections.

Correction, Nov. 7, 2018: This post originally misspelled Rep. Chellie Pingree’s last name.