AUGUSTA — What a ranked-choice presidential primary in Maine would look like next March remained largely uncertain Tuesday, a day after the state Senate passed a bill approving the system on a nearly party-line, 20-12 vote during a one-day special session.

Gov. Janet Mills, a Democrat who won her party’s gubernatorial nomination in the nation’s first use of ranked-choice voting to decide a statewide race, is not saying whether she will sign or veto the bill.

It took eight days for Maine’s secretary of state to collect and tabulate ballots in the 2018 primary, declaring on June 20 that Mills had won the June 12 election. In March, Democrats could have a slate of as many as 20 presidential candidates for voters to rank, which could make for a long and complicated tabulation.

On Tuesday, Mills’ staff would say only that she is considering the measure and has 10 days to decide whether to sign the bill. The Maine House approved the bill during its regular session earlier this year.

Secretary of State Matt Dunlap, also a Democrat and the state’s top election official, said his office is proceeding under the assumption that the state will conduct its first ranked-choice presidential primary in March.

It’s unclear, however, how the state will pay for the election, which is expected to cost about $100,000, Dunlap said. When the Legislature returns for its second session in January, it may have to pass another measure appropriating funds to cover the cost.

Earlier this year, the Legislature passed a law switching Maine back to a presidential primary vote and away from a party caucus system that was fraught with problems for both Democrats and Republicans in 2016.

Dunlap says his office has the expertise to conduct the March primary by ranked choice, having now completed two such elections, but would incur expenses for items such as renting tabulation equipment and contracting with a courier service to bring ballots to Augusta for counting.

The process allows voters to rank contenders in races with three or more candidates in order of preference on the ballot. If any candidate receives 50 percent or more of the vote on the first tally, he or she is declared the winner and the election is over. If no one receives a majority, however, the candidate with the least number of votes is eliminated and that candidate’s votes are reallocated to the candidates that their supporters ranked second.

That process continues – with candidates eliminated from the bottom up and their supporters’ votes redistributed – until one candidate secures a majority of the remaining vote pool.

Despite the fierce partisan divide over ranked choice, there is little evidence to show that the system benefits either party. In Maine, support for ranked-choice voting among many Democrats is rooted in anguish over the election of Republican Gov. Paul LePage, who was elevated to the Blaine House in a three-way race in 2010 that saw him win 38 percent of the vote.

Because primary elections are mainly functions of the established political parties, Democrats and Republicans still will have broad discretion in how they use the results of a ranked-choice primary to assign delegates to their respective party conventions, where presidential candidates will ultimately be nominated for the race.

How they do that will be up to state and national party committees. Although Dunlap’s staff will be able to determine a winner using the ranked-choice process, that candidate is unlikely to be awarded all the delegate votes from the party.

Democrats already have signaled that they will still apportion delegates to candidates who receive as little as 15 percent of the vote.

Alex Stack, a spokesman for the Maine Democratic Party, said Tuesday that party officials were awaiting Mills’ decision on the legislation before determining how they would proceed.

Democratic Party leaders in at least six other states have said they will use ranked-choice voting for their primaries or caucuses, including early voters in Iowa and Nevada and all voters in Hawaii, Alaska and Kansas, according to the nonprofit election website FairVote.org.

In those states, the process would allow any candidate receiving at least 15 percent of the vote to be apportioned state delegates for the national convention vote. But the rules do not say that the delegates would have to stay with the candidate should they not prevail at the national convention.

Switching from the caucus system to a March presidential primary in Maine is expected to cost local municipalities about $950,000 on top of the $100,000 for the state’s expense, Dunlap said.

State House Republican leaders, who oppose ranked-choice voting and its use in the primary, said they were caught off guard Monday when the bill was brought to the floor of the Senate for an enactment vote.

“We just didn’t see it coming, to be quite honest with you,” said Sen. Jeff Timberlake, R-Turner, the Senate’s assistant minority leader. The roll call on the bill saw all 11 Republicans in the chamber vote against the measure. They were joined by one Democrat, Sen. Bill Diamond of Windham, who has previously served as Secretary of State.

Timberlake said Republicans believed the bill should have stayed in the Legislature and been sent to the Appropriations and Financial Affairs Committee for funding and not sent to the governor’s desk.

“It doesn’t have a funding source, so I’m not sure how they managed to send to it directly to her desk,” Timberlake said. But Timberlake also said its unclear how the parties will use ranked choice in apportioning delegates.

“The parties can do whatever they want,” he said.

Whether Republicans will have a contested presidential primary in March also is unclear, although both former Massachusetts Gov. William Weld and former Illinois Congressman Joe Walsh have said they intend to challenge President Trump for the party’s nomination. Challengers to  would need to be declared by Nov. 1 in Maine.

Maine Republican Party Executive Director Jason Savage said party leaders will take a few weeks to reach a decision on how to proceed regarding the presidential primary. Savage criticized Democrats and Senate President Troy Jackson of Allagash over the cost of the election and how the measure was passed.

“It’s shameful that Troy Jackson told this paper he was not going to bring the RCV bill up during the special session, then went and rammed it through at the last moment,” Savage said in an email late Tuesday. “The whole fiasco is reckless and dishonest and Sen. Jackson still has not figured out how to pay for it. Hopefully, Governor Mills will be a voice of reason here.”

Republicans have been steadfastly opposed to ranked-choice voting, fighting it both in the Legislature and in the courts without success.

Besides the 2018 Democratic primary, Maine also used ranked-choice voting in the 2nd Congressional District election in 2018 that saw Democratic challenger Jared Golden unseat Republican incumbent Bruce Poliquin after the ranked-choice tabulation of votes. Poliquin lost a federal court challenge of the outcome and later withdrew his appeal on the case.

Dunlap said that in the case of primary elections, the parties would make the rules on what they do with the results from the “cascade” of ranked-choice votes that will be tabulated by his office on primary day.

“Party nominations are not the same as elections,” Dunlap said. “There are still a lot of unknowns. Everything we are doing, we are doing brand new.”