Maine Gov. Janet Mills speaks during a news conference launching an Outdoors Recreation Initiative on Wednesday, July 24, 2019, in Salt Lake City. Credit: Rick Bowmer | AP

AUGUSTA, Maine — Gov. Janet Mills said Friday she’s still reviewing a bill passed by the Maine Legislature to extend ranked-choice voting to presidential primaries and general elections in part over its effect on the 2020 nominating races and potential cost concerns.

Mills has five more days to decide whether to approve, veto or hold the bill the Senate voted on Monday. If she signs it or lets it pass into law without her signature, the bill would take effect in time for the March primary.

The Democratic governor said before being elected in 2018 that she would support a constitutional amendment to extend the method’s use to general elections for governor and the Legislature — Maine Senate President Troy Jackson, D-Allagash, the bill’s sponsor, said Mills did not want the bill to move forward on Monday.

It passed in a 20-12 vote in the Democratic-led Maine Senate near the end of a one-day special session focused on bond proposals with no discussion. In another key 2019 change, Maine lawmakers allowed parties to switch from party-run presidential caucuses to state-run primaries.

Mills said after an event with the Kennebec Valley Chamber of Commerce she is still “reading the bill carefully” and trying to determine how it would affect the presidential primaries.

“There are six other states that are apparently looking at ranked-choice voting are all caucus states,” she said. “I’m not aware of any other state looking at it for the primary.”

Mills was referring to the Democratic parties in Iowa, Hawaii, Kansas, Alaska, Wyoming and Nevada that have plans to use ranked-choice voting in their crowded race for the nomination to face President Donald Trump, according to FairVote, an electoral reform group.

However, those changes aren’t official yet: The Democratic National Committee has taken no stance on using the voting method in its nominating race and each state — including Maine — will have to have their delegate allocation plans approved by a party committee.

FairVote has said Democrats would likely allow a form of ranked-choice voting based on the party’s threshold of 15 percent of votes to qualify for part of a pool delegates. If a voter’s first-choice candidate has 15 percent of votes or more, their vote would remain with that candidate.

But if their first choice is in last place and below the threshold, their vote would move to a second choice. That would continue until all remaining candidates are at or above 15 percent and the delegate pool would be split proportionally.

On Friday, Mills also said she needs more information on what a line in the bill referring to the “general elections for presidential electors” means. She called cost “a factor as well,” since Jackson’s bill provided no new money to the secretary of state to run a ranked-choice election.

State parties are split on whether they’ll use the primary in 2020, with Democrats saying they will and Republicans saying they’ll decide between that and a caucus in September.