PORTLAND, Maine (AP) — For the first time in U.S. history, voters will use ranked choice voting to determine their pick for president of the United States.

Maine's use of ranked voting comes as Alaska and Massachusetts voters consider statewide votes to adopt the voting method. In Maine, it applies to this year's presidential and U.S. Senate races.

The method works like this: Voters can rank the candidates on their ballot in order of preference. If no candidate breaks 50% of the popular vote, the bottom finisher is eliminated, and voters’ second choices come into play. The tabulations continue until a candidate achieves a majority of the total votes.

Ranked voting arrives on Maine’s presidential ballots in a year when three of the state’s four electoral votes could be up for grabs.

The state is one of only two that apportions electoral votes — one each — by congressional district, of which Maine has two. The statewide vote, which is worth two electoral votes, could also be in play. The huge, largely rural 2nd Congressional District is competitive for President Donald Trump and former Vice President Joe Biden, but the 1st Congressional District in southern Maine is safely Democratic.

The U.S. Senate race is a closely watched one that includes four candidates and is expected to be tight. They are Republican Sen. Susan Collins, Democratic Maine House Speaker Sara Gideon and independents Max Linn and Lisa Savage.

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THE BIG COUNT

Maine Secretary of State Matthew Dunlap has said he hopes to declare whether another round of tabulations will be necessary in any races by the end of Election Day.

The state would then send out couriers to collect the ballots, which must be in locked and sealed ballot boxes, said Kristen Muszynski, a spokesperson for the Maine Department of the Secretary of State. The ballots would likely be collected through the weekend and the counting could commence in the state capital of Augusta on Monday or Tuesday of the following week, she said.

The counting itself can take a week to two weeks, Muszynski said. She said voters shouldn't take the time frame as an indication that there's a problem with the counting.

“It's going to take time, and that doesn't mean anything's wrong,” she said.

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HOW WE GOT HERE

Voters in the state approved the adoption of ranked voting in a 2016 referendum drive. The method then withstood legal challenges.

The method propelled Democratic Rep. Jared Golden to victory over Republican incumbent Bruce Poliquin in 2018.

Maine doesn't use the method for state races, like governor, because it runs afoul of the Maine Constitution.

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WHY RANKED CHOICE?

Fans of ranked voting began a drive to adopt the method in Maine after the state twice elected Republican Gov. Paul LePage with vote totals that were less than 50%. They said the method eliminates the possibility of “spoiler” candidates and encourages voters to be more informed.

Opponents, including the Maine Republican Party, have said ranked choice voting is too confusing and violates the principle of one person, one vote. They sued unsuccessfully to try to stop the state from using ranked choice voting for president this year.