× Expand J. Scott Applewhite/AP Images Senator Susan Collins takes questions from reporters at the Capitol.

As she travels around Maine gauging her re-election prospects, Susan Collins is bound to face some very angry women still seething about her vote to confirm Brett Kavanaugh for a lifetime Supreme Court appointment. The Kavanaugh hearings lit a fire under many of her constituents, one that has been smoldering at least since 2016. It's now jumped her last political firebreak, her reputation as a reasonable Republican.

With the repercussions of Donald Trump's victory made plain by that single vote, the unprecedented outpouring of political engagement in Maine in 2018 produced a Democratic trifecta and put Collins’s seat in play. With the path to a possible Democratic Senate majority winding through Maine, candidates who have been biding their time are jumping into what promises to be a volatile race to knock off Collins.

This stands in contrast to other Senate races, where Democrats have failed to secure top-tier opponents and lost some possible challengers to the presidential race. The pile of worthy candidates in Maine is a testament to Collins’s lagging popularity in a state she once dominated.

Expected to announce her candidacy in the coming weeks, according to a recent HuffPost report, is Sara Gideon, the Speaker of the Maine House of Representatives. If she follows through, Gideon would jump to the head of the line of Collins’s opponents. The Speaker would likely draw most of her support from the liberal population centers in the coastal and southern regions of the state. Collins continues to have a strong base of support among Republicans and conservatives, especially in the rural northern reaches of Maine.

Gideon has some work to do to raise her statewide profile, especially compared to a longtime political veteran like Collins—which could account for the results of a March Pan Atlantic Research poll of likely 2020 voters. In a hypothetical matchup, Collins bested Gideon, 51 percent to 29 percent.

Another recent entrant and strong contender is former 2018 gubernatorial candidate Betsy Sweet of Hallowell, near Augusta. Sweet, a longtime progressive lobbyist, came in third in the Democratic gubernatorial primary. The other declared candidate is Bre Kidman, a lawyer from Saco, south of Portland. A second tier of possible candidates includes Maine Secretary of State Matt Dunlap and Rosa Scarcelli, an affordable-housing developerwho ran for governor in 2010.

U.S. Representative Chellie Pingree has been touted as another maybe, as has her daughter, Hannah, a former Maine House Speaker who currently heads up a new state office of innovation, a strategic planning agency. But the elder Pingree, who represents Maine's First District (and whom Collins beat in 2002 to retain her Senate seat), claims she has the job she wants and so does her daughter. “I'm pretty happy in the majority in the House,” she told Bloomberg Environment. “I don’t think either one of us is going to be her challenger.”

A Crowdpac fund set up for a 2020 Democratic challenger has raised nearly raised $4 million, which about matches what Collins has in her war chest. (Most of her funds have come from out-of-state donors.) The Senate primaries and the general-election contest will be subject to ranked-choice voting, which Maine used for the first time last year.

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Yet no matter who Collins's opponent is, the contours of the 2020 Senate race are likely to be determined by national developments. The biggest wild card affecting Collins's chances is Trump himself, who is unpopular in Maine: 53 percent of likely voters in the March poll said they would “definitely not” vote for Trump; 88 percent of Democrats and nearly 67 percent of independents said no way, compared to about 11 percent of Republicans.

Meanwhile, Collins continues to baffle. Last week, she came out against the nomination of a conservative lawyer who has opposed abortion and LGBT rights. She also opposed the nomination of Wendy Vitter, a Roman Catholic Archdiocese of New Orleans attorney and the wife of former Senator David Vitter of Louisiana, for a federal district court seat. But Collins’s votes to confirm dozens of the president’s other nominees for federal court vacancies are being held up as Exhibit A of her willingness to support abortion opponents in service of the Trump administration’s push to remake the courts.

Her difficulties in Maine will be compounded by running in a new political environment that spotlights her Kavanaugh vote. The staunchly pro-choice Democratic Governor Janet Mills has signed two bills that expand abortion access: one that requires public and private insurers to cover abortions and effectively provides abortions for women under Medicaid and a second that allows nurse practitioners and others, in addition to doctors, to perform medication abortion and other procedures.

Abortion is just one hurdle. Mills has also signed a landmark state internet privacy protection law, the first in the country to counter federal legislation that allows internet service providers to sell their customers’ personal data—which Collins had supported. The senator’s vote for Trump’s tax plan, which has done little for middle- and low-income Americans, will come under fire in a state where progressive advocates have called for the repeal of state tax cuts on wealthy Mainers. Her record on energy and environmental issues is coming under scrutiny, in part, because of her support for Kavanaugh, who has favored restricting the Environmental Protection Agency’s regulatory powers.

Collins, who has vanquished past Democratic challengers by healthy margins, has not yet formally announced her candidacy. She is decidedly the GOP front-runner; so far only a Republican blogger plans to primary her. But job satisfaction in a Senate being degraded by the party-over-country partisanship of Mitch McConnell isn’t what it used to be. In 2012, fellow Mainer Olympia Snowe, Collins’s Republican colleague in the Senate, retired after nearly 20 years, citing that very problem. “I have spoken on the floor of the Senate for years about the dysfunction and political polarization in the institution,” she wrote in The Washington Post. “Simply put, the Senate is not living up to what the Founding Fathers envisioned.”

If Collins decides not to run, the Maine Republican Party might just turn to Paul LePage, one of the few campaign trail–tested Republicans with statewide name recognition, who continues to enjoy a strong base of local support. The infamous former governor is currently tending bar at a Boothbay Harbor restaurant.