Sen. Susan Collins Susan Margaret CollinsDemocratic senator to party: 'A little message discipline wouldn't kill us' Poll: 57 percent of Americans think next president, Senate should fill Ginsburg vacancy On The Trail: Making sense of this week's polling tsunami MORE (R-Maine) downplayed speculation that she could lose her Senate seat in 2020, saying she's confident she would win reelection.

“The people of Maine have known me, and they know that I have been a hardworking, independent advocate for them, who votes with integrity,” Collins said, according to Bloomberg.

“Should I choose to seek reelection, I’m confident it will go well," she continued.

ADVERTISEMENT

Collins, who won reelection by over 30 points in 2014, now faces a tough race, which The Cook Political Report has shifted from a "lean Republican" to "toss-up" election.

Maine House Speaker Sara Gideon (D) has launched a challenge against Collins, raising over $1 million in the first week of her campaign.

The incumbent senator has been critical of President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE but faced backlash in 2018 for voting to confirm now-Supreme Court Justice Brett Kavanaugh Brett Michael KavanaughTrump plans to pick Amy Coney Barrett to replace Ginsburg on court Collins trails challenger by 4 points in Maine Senate race: poll SCOTUS confirmation in the last month of a close election? Ugly MORE in 2018.

Gideon has hit Collins over the decision, saying in her campaign launch video that it “put women’s control of their own health care decisions in extreme jeopardy.”

She recently defended her decision, telling The New York Times last month that she did not regret her vote "in the least."