It is not clear yet what legal arguments might be made against ranked-choice voting if the law were challenged as a result of the outcome in Maine’s 2nd Congressional District race.

“I don’t think there’s any way they can win,” Rob Richie, president of Fair Vote, a Maryland group advocating election reform, said Thursday.

He said court cases around the country for years consistently have ruled in favor of ranked-choice voting arrangements. Bringing a case would paint someone as “a sore loser” with a frivolous case, Richie said.

Maine Supreme Judicial Court Justice Donald Alexander said in an oral argument in the spring that one theory could be that the system violates the 14th Amendment’s equal protection clause, which has led the “one person, one vote” standard in American elections.

It is an argument that has been made before — and always shot down.

In Minnesota, for example, the state’s highest court found in 2009 that because “every voter has the same opportunity to rank candidates” and “each round every voter’s vote carries the same value,” there is no constitutional problem.

A U.S. Court of Appeals once ruled that ranked-choice voting is fine because “each ballot is counted as no more than one vote at each tabulation step.”

A Massachusetts court ruled in 1996 that voters are not denied equal opportunity with ranked-choice voting because all voters have the same chance “to cast a ballot at the same time and with the same degree of choice among candidates.”

Though no state has used ranked-choice voting for a federal election before, some states have required a candidate win a majority before taking office, typically relying on special runoff elections between the two front-runners if nobody gets 50 percent or more.

In Mississippi and other Southern states that have runoff elections, overseas ballots have included a ranked-choice option for the general election so any runoff races are not delayed by the required timelines to allow military personnel to vote from faraway locales, Richie said.

Lewiston elects its mayor with a runoff election that follows the same model. If there is no majority winner, the two candidates with the most votes on Election Day are pitted against each other in a special runoff election a month after the general election.

Without that system in Lewiston, Ben Chin, who won a plurality in each of the past two mayoral races, would have won. He lost both times in the runoffs.

Ranked-choice voting is like an instant runoff, with a second election essentially built into the system.

Under a ranked-choice system, rankings do not come into play unless no candidate gets more than 50 percent — a majority — of the votes.

If that happens, each vote cast for the least-popular candidate in the race is redistributed to the contender listed as the next choice on that voter’s ballot, if the voter ranked another candidate.

That process continues until one of the candidates has more than half of the votes, when a winner is declared.