In the most expensive House race in Maine history, candidates and their supporters spent more than $31 million in Maine’s 2nd Congressional District race, with Democrat Jared Golden and supporters spending $131 per vote in his successful bid to unseat incumbent Republican Bruce Poliquin.

Golden and his supporters spent $18.3 million in the race, while Poliquin and his supporters spent about $13 million, or $95 per vote.

The total spending was almost twice the $17 million spent in 2016, when Poliquin fended off Democratic challenger Emily Cain.

Maine’s high-profile governor’s race, with Democrat Janet Mills beating Republican Shawn Moody, did not set any spending records. The total spent by all four candidates and their supporters was just about $17.5 million, less than the record $19 million spent on the 2014 governor’s race.

Golden was declared the winner Thursday in a closely watched race that was part of a widespread “blue wave” effort to flip Republican seats across the country. It drew significant outside spending, particularly by powerhouse Democratic-backed groups.

That financial backing was key to Golden building name recognition, according to James Melcher, a political science professor at the University of Maine at Farmington.

“Most of the time challengers to incumbents don’t have the kind of money Jared Golden had,” Melcher said. “It’s astonishing to see a challenger with more money than an incumbent. It’s really quite unusual.”

In the final ranked-choice tally there were 139,231 votes for Golden versus 136,326 votes for Poliquin, a margin of 2,905 votes.

In Maine’s 1st Congressional District race, incumbent U.S. Rep. Chellie Pingree won after spending just over $1 million, or $5.21 per vote, almost all of it from her campaign. Independent challenger Martin Grohman spent $258,087 or $8.73 per vote, and Republican Mark Holbrook spent $38,141, or 35 cents per vote, in their losing bids to unseat Pingree.

In other Maine races:

• Independent Angus King spent about $4.5 million, or $13.07 per vote, to hold on to his U.S. Senate seat. Challenger Eric Brakey, a Republican, and his supporters spent about $1.9 million, or $8.47 per vote, and Democrat Zak Ringelstein spent $327,341, or $5.06 per vote.

• The four-way race to succeed Gov. Paul LePage drew intense campaigning and big dollars, but the spending didn’t surpass the 2014 gubernatorial race when challenger Eliot Cutler poured millions of his own money into his second attempt to beat LePage. Spending in that race, between Cutler, LePage and former U.S. Rep. Mike Michaud, exceeded $19 million – more than double the $9 million spent by LePage, Cutler and Democrat Elizabeth Mitchell in the 2010 gubernatorial race.

This year, Democratic-backed outside groups spent big in the governor’s race, with Mills and her supporters spending $10.7 million, or $33.56 per vote. Moody and his backers spent almost $4.9 million, or $18.04 per vote. Independent Terry Hayes, who ran as a Clean Elections candidate, spent $1.4 million, or $36.80 per vote, and fellow independent Alan Caron spent $610,472 before withdrawing in the final days before the election.

• Ballot Question 1, a home health care initiative that was soundly defeated 63 percent to 37 percent, drew $2.2 million in spending. By comparison, the successful 2016 campaign to legalize recreational marijuana spent $2.8 million.

• In the 2nd District, the bulk of the spending was by outside groups. Golden’s campaign spent $4.2 million through Oct. 17, according to federal campaign finance reports, but outside groups spent more than three times that amount – $14 million – to back him. Poliquin spent $3.2 million and outside groups spent about $13 million. Those candidate campaign spending figures only include expenditures through Oct. 17, however, and will increase when final campaign finance reports are filed in mid-December.

Spending in the race will likely increase by almost $2 million, the amount of money Golden and Poliquin had on hand at the last reporting period, plus contributions received in the final weeks of the race.

As of Oct. 17, Poliquin had about a quarter-million dollars on hand to spend, and his campaign raised another $740,000 in the final weeks before the election. Golden had $450,000 cash on hand and raised another $240,000. If they spent all that money, Poliquin would break the $100-per-vote threshold, spending $102.23 per vote, while Golden’s spending would result in $136 per vote.

During the campaign, both candidates decried the amount of money pouring into the race from outside groups, virtually all of it for advertising opposing their favored candidate.

Outside groups reported spending $12.6 million opposing Poliquin and $9.2 million opposing Golden. By comparison, outside groups spent only about $560,000 supporting Poliquin and $1.5 million supporting Golden.

This federal election cycle, with multiple competitive races across the nation, set new records for the number of television ads aired, according to the Wesleyan Media Project, which tracks political advertisements. The group found that Maine’s CD22nd District race sparked 30,984 television ads, the fourth-highest volume of ads of any House race nationwide. By comparison, a Montana House race that fueled almost 70,000 ads set the record.