Maine Sen. Susan Collins was once one of those rare politicians who received rave reviews across party lines. Democrats loved her because she is pro-choice and works across party lines. Republicans loved the independence that let the party hold a seat in New England.

That’s changed since Collins won 68 percent of the vote in 2014. In a Morning Consult poll released this month, she is underwater with 45 percent approval and 48 percent disapproval, making her second to Mitch McConnell as America’s most unpopular senator. Adding insult to injury, her fellow Maine senator, Angus King, an independent who caucuses with the Democrats, is the most liked senator in the country.

Some might argue that Collins’ stunning fall from grace stems from her support for Donald Trump, but it’s really her own doing after 22 years having it both ways.

Brett Kavanaugh was her crucible. His confirmation to the Supreme Court last year hinged on Collins’ vote. After allegations of sexual misconduct surfaced against Kavanaugh, she was a final holdout, keeping everybody in suspense for several days before finally taking to the Senate floor to declare in a nearly hour-long speech that she would support Kavanaugh.

For many female voters, this was a bridge too far for the having-it-both ways decision-making they associate with Collins. On the one hand, she found the testimony from Kavanaugh’s accuser, Christine Blasey Ford, “to be sincere, painful, and compelling.” On the other hand, she concluded Ford’s claims did not meet the threshold of “more likely than not.”

Her lengthy public deliberation over Kavanaugh and, before him, Neil Gorsuch, ended with yes votes coupled with her personal assurances to the pro-choice community that both men serving lifetime appointments on the Supreme Court are more centrist than they appear and are unlikely to overturn Roe v Wade, the 1973 ruling that legalized abortion.

The price for Collins’ vote is coming due. Six pollsters found that opposition to Kavanaugh mounted from July of 2018 to mid-October, when he was sworn in, with one survey taken after he was confirmed finding more people (42 percent) saying Ford had been treated more unfairly by the Senate Judiciary Committee than Kavanaugh (33 percent), according to a deep dive by public opinion expert Karlyn Bowman published in the July issue of the conservative American Enterprise Institute’s Political Report.

“Obviously, the Kavanaugh vote was a very big deal,” says Jennifer Duffy with the non-partisan Cook Political Report. “Some people will never forgive her for that vote, mostly women—but also moderate Republicans and moderate Democrats who crossed the line and voted for her.”

Activists have already raised over $4 million to back the Democrat who challenges Collins, and NextGen America, created by hedge fund billionaire (and now presidential candidate) Tom Steyer, just announced it will spend $1 million in Maine to try and unseat Collins.

“This will be a very expensive and closely contested race,” Duffy told the Daily Beast, not only because of Collins’ own vulnerability but also the strength of her likely opponent, Maine House Speaker Sarah Gideon. “Democrats are excited about her in a way I haven’t seen them excited about anybody in a long time.”

Gideon, 47 and the mother of three, announced last month in an effective video from her handsomely appointed kitchen that went straight at Collins and the doubts dogging her, saying, “At one point maybe she was different than some of the folks in Washington. But she doesn’t seem that way anymore.”

Gideon has to get through a primary which won’t be held until June of 2020, but so far she is the only candidate in the Democratic primary field who has held major elective office, and she enjoys widespread support in her party. In her announcement video, she recalls how she first ran for office after hearing a message on the family’s answering machine in 2009 trying to recruit her husband, Ben, to run for town council. “I thought to myself, actually I think that’s a job that I can do.”

Gideon has been a champion for issues Democrats care about, and with a Democratic governor, Janet Mills, elected last year, Gideon has a roster of legislative accomplishments she can tout, including expanding abortion rights in the state. In her video, she alludes to the fact that Collins had the best fundraising quarter in her career after her Kavanaugh vote, saying that the support “may be paying off for her, but it’s put women’s control over their own health-care decisions in extreme jeopardy.”

For a time, there was speculation that Collins, 66, might opt out of the fight and choose to retire. But that isn’t happening. “I see a different Collins,” says Duffy. “In the past, she would start her campaign after Labor Day and not spend too much time raising money. This time, she’s all in—she’s fundraising aggressively, and she is really all over the state.”

Democrats shouldn’t be lulled by her high disapproval number, or by Mitch McConnell’s for that matter. A large part of their disapproval comes from Trump supporters who would never vote for a Democrat, and with him at the top of ballot they’re unlikely to stay home or vote for someone else—which would mean that Collins only needs support from about 15 percent of Democrats to put her over the line.