A leading conservative think tank is pushing Democratic Gov. Janet Mills to veto a bill passed by the state Senate this week to expand ranked-choice voting to presidential primaries.

If Mills signs the bill or it becomes law without her signature, Maine will be the seventh state to use ranked-choice voting in the upcoming Democratic presidential primary, joining Iowa, Nevada, Hawaii, Alaska, Kansas and Wyoming.

A spokesman for Mills said Thursday that she was still considering the legislation

In a letter to Mills, the Maine Heritage Policy Center points to its own analysis of ranked-choice voting in 96 jurisdictions in the United States as evidence that the system doesn’t work the way proponents say it does.

“In the average ranked-choice voting election, 11 percent of ballots are thrown out due to ballot exhaustion,” the nonprofit said in its letter to Mills, citing its 40-page analysis. “This causes the average winner of these elections to win with a fake majority of the votes cast on Election Day approximately 61 percent of the time.”

Ballot exhaustion “occurs when a ballot is no longer countable in a tally as all of the candidates marked on the ballot are no longer in the contest,” according to Ballotpedia, a nonpartisan nonprofit that compiles information on U.S. politics and elections. “This can occur as part of ranked-choice voting when a voter has ranked only candidates that have been eliminated even though other candidates remain in the contest, as voters are not required to rank all candidates in an election.”

The center’s analysis, titled “A False Majority,” also says that voters who don’t rank their candidates or who may have mismarked their ballots for rounds of counting beyond the first tabulation are not having their votes counted, suggesting that such voters are being disenfranchised.

But supporters of the ranked-choice system are urging Mills to sign the bill, which would have primary voters in the March presidential primary rank their candidates by preference.

The measure passed the Senate Monday on a 20-12 vote, with 11 Republicans and one Democrat opposed. It now sits on Mills’ desk. She has eight days left to make a decision on the bill, which she can sign, veto or allow to become law without her signature.

If she signs the bill, it will put the law in play for the presidential primaries in March 2020.

“Under current election law, ranked-choice voting is used in every other federal primary and general election (in Maine)” said David Farmer, a spokesman for the Committee For Ranked Choice Voting. “It makes sense to add it for the presidential primary election, which includes an unprecedented number of candidates.”

That primary is largely expected to be a Democratic Party affair, with more than 20 candidates now vying for the party’s nomination to challenge President Trump.

The ranked-choice 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, the candidate with the fewest 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.

Maine was the first state to implement ranked-choice voting in statewide federal elections and primary races, in 2018. So far the process has been applied in only two statewide contests – the 2018 Democratic primary for the governor, won by Mills, and in the 2018 general election contest for Maine’s 2nd District congressional race, which was won by Democratic challenger Jared Golden.

Ranked-choice voting is not used in Maine for the general election contest for the governor’s office or the Legislature, based on an advisory opinion of the state’s Supreme Judicial Court, which said the Maine Constitution calls for those elections to be determined by a plurality only.

Kristen Muzsynski, a spokeswoman for Maine Secretary of State Matt Dunlap, the state’s top election official, said the Maine Heritage Policy Center’s analysis is accurate in its assessment that a winner in a ranked-choice election is determined by a majority of the votes tabulated in the final round of counting.

“By the time you get to the final round, some ballots have been exhausted (those of people who voted for candidates who didn’t make it to the final round), so the “majority” to which we are referring is not reflective of the majority of the total ballots cast,” Muszynski wrote in an email to the Portland Press Herald. “It is the majority of the ballots that are still active in the final round.”

She said the Secretary of State’s Office always has made that known in its informational material about ranked-choice voting.

However, Muzsynski said that doesn’t mean any voter’s ballot is being “thrown out” or not counted.

“Just like in plurality voting, your vote counts, even if you didn’t vote for the person who eventually wins,” she said in an email.

In both plurality and ranked-choice voting, voter behavior is a bigger factor than the voting system in determining whether any ballot will be invalidated, Muszynski said.

It’s a point not lost on the Maine Heritage Policy Center, said Jacob Posik, the center’s communications director. He agreed that voter behavior may be to blame for any invalidated ballots, but said the confusion surrounding the ranked-choice voting system is driving that behavior.

Posik said voters who don’t rank their candidates or who rank only one candidate are discounting their own ballots. He also noted that some of that behavior was promoted by the Maine Republican Party, which urged voters in the last election to select only one favorite candidate, even in ranked-choice races.

“The GOP telling people to only rank one candidate doesn’t really help,”Posik said.

Posik said he would encourage people to rank candidates in a ranked-choice election, if that’s the system, but said the complexity and vagaries of the system aren’t fully grasped by many voters, which may discourage participation.

“I don’t care who wins,” Posik said. “But I care that I think voters don’t truly understand how this system works.”

Posik added that ranked-choice voting also isn’t doing what its supporters have promised it would do in terms of moderating an increasingly overheated political environment or removing dark-money political attack ads.

The center’s analysis also points to a handful of places where ranked-choice voting ordinances or laws were repealed after voter dissatisfaction.

But supporters of the system pointed out that Mainers approved ranked-choice voting in a statewide referendum and then voted again to keep it with a people’s veto that overturned the Legislature’s repeal of the system in 2016.

“Everyone who votes has their ballot counted,” Farmer said, “and based on their personal choice, their ballot is continued to be counted until a winner is declared. Voters have used ranked-choice voting in Maine, they like the system and understand how it works.”

Rob Richie, the president and CEO of FairVote, a Maryland-based nonprofit that advocates for election reform and supports ranked-choice voting, said despite any minor flaws, ranked-choice voting is still a better system than plurality voting.

Richie said that just because some voters choose candidates who are not in the final rounds of counting, that doesn’t mean they are disenfranchised.

“And it doesn’t affect the fact that (with ranked-choice voting) when you narrow the choice to two, this one got a majority of what was left and that’s part of the story,” Richie said. “Anybody that wants some kind of perfection can go to a sort of electoral heaven, I’m not sure it exists, but where everything works out perfectly –  but is this an improvement over what we had? I think it is.”