Long regarded as a blue state, Maine had been shifting in recent years towards red, even with a Partisan Voting Index score of D+3. In 2016, Hillary Clinton’s three percent margin of victory was the narrowest for a Democrat since 1988, when Republicans last won the state. Clinton carried Maine’s two at-large electoral votes with a plurality and won Maine’s 1st Congressional District, while Trump won Maine’s 2nd District, the first Republican to do so since 1988.

All of that changed in 2018 when Maine elections were conducted with ranked-choice voting, as opposed to a simple plurality. Maine voters had passed a referendum approving the change in 2016, followed by a June 2018 referendum sustaining the change. U.S. Senator Angus King, an Independent who caucuses with the Democrats, won the 3-way Senate race with 54.3 percent of the vote in the first round of voting, so the instant runoff was not needed. It was used, however, in the 2nd Congressional District, where incumbent Republican Congressman Bruce Poliquin ultimately lost to Democratic challenger Jared Golden. It was the first time in over 100 years that an incumbent has lost Maine’s 2nd District, and Poliquin was the last Republican representing New England in the House.

In 2018 Democrat Janet Mills became the first woman ever elected as Maine’s governor. In a strong repudiation of the regressive policies of her predecessor, Paul LePage, Mills is also the first Maine governor to be elected with at least 50 percent of the vote since Angus King in 1998 and the first to win at least 50 percent of the vote for a first term since 1966. Mills won the election with 50.9 percent compared to 43.2 percent for her Republican opponent Shawn Moody. One of Mills’ first acts as governor was to sign an executive order to carry out the expansion of Maine’s Medicaid program as mandated by a 2017 referendum, something LePage had refused to do. Also in the 2018 elections, Democrats gained control of the State Senate, flipping a 17-18 minority into a 21-14 majority, and the State House’s Democratic majority increased from 73-70 with seven independents and one vacancy to 89-57 with five independents.

We are following the Senate race in Maine because Senator Susan Collins is one of two Republican senators on the ballot this cycle in states that Clinton won. Also our research indicates that mobilization of Democratic voters who might otherwise not vote can make the difference in this race.