For the first time in U.S. history, a controversial voting system known as "ranked choice" is being used to decide a federal election.
It's happening in Maine, which adopted the system in 2016.
Rather than marking a single candidate, each voter ranks them all, assigning a first-place vote, a second-place vote and so on down the ballot.
If no candidate receives more than 50 percent of the vote, the lowest-ranked one is eliminated and the results are recalculated. The process is repeated until one candidate reaches at least 50 percent.
In Maine's 2nd Congressional District, a rural area north of Portland that backed Donald Trump in 2016 and President Barack Obama in 2012, none of the four candidates on the ballot got that majority. Bruce Poliquin, the Republican incumbent, was narrowly leading Jared Golden, a Democratic state representative, 46.2 percent to 45.5 percent.
Maine Secretary of State Matthew Dunlap said Thursday that the instant runoff process had started and that he expected a winner to be announced next week. The congressional district is the largest east of the Mississippi River in terms of land area, and private couriers contracted by the state were picking up memory sticks as well as paper ballots from towns that still count votes by hand.
Sponsored Video Stories from LifeZette
"It's been a tortured, long journey with ranked choice," Dunlap said in an interview. "Now it's going to get a little longer."
Maine is the only state to adopt the voting system, though several cities across the country use it in local elections. It is similar in some sense to the runoff elections used in some states -- mostly in the South -- when a candidate fails to win a majority of the total vote.
Proponents say that ranked choice prevents candidates from winning office through a strategy of divide and conquer.
Maine has long had an independent streak, creating a political climate in which ballots are usually filled with independents and third-party candidates. Before the narrow passage of the ballot measure that established the new voting system, nine of the previous 11 gubernatorial elections were won by candidates who had failed to get a majority of the vote.