Sen. Susan Collins, R-Maine, is surrounded by reporters as she heads to vote at the Capitol in Washington, Wednesday, Nov. 6, 2019. Collins is expected to make a formal announcement on her reelection plans later this week. Credit: J. Scott Applewhite | AP

AUGUSTA, Maine — U.S. Sen. Susan Collins, a Republican, is expected to make a formal announcement this week on whether or not she’ll run for re-election for a fifth term next year in a nationally targeted 2020 race in a Democratic-leaning state.

Maine’s senior senator told Politico on Tuesday she will fulfill her promise to announce the decision by the end of fall — which comes on Saturday. Collins spokesperson Kevin Kelley confirmed the announcement this week is coming but provided no further details.

It’s almost certain Collins will run again. While Collins has demurred on a formal kickoff, she has filed to run again and her campaign is running at full tilt, raising $8.6 million by September’s end, more than any politician in Maine history. More than $8 million has been spent in advertising on the race — an unprecedented total in the state this early.

Collins sailed to victory in her last race in 2014, but she faces a targeted race from Democrats next year after her 2018 vote for U.S. Supreme Court Justice Brett Kavanaugh. She has rallied Republicans — including Gov. Paul LePage, who was once skeptical of her — to her side in a heavily partisan and nationalized race over the Maine seat.

House Speaker Sara Gideon, D-Freeport, is the front-runner for the Democratic nomination, though she faces a four-way June primary with Hallowell lobbyist Betsy Sweet, Saco lawyer Bre Kidman and former Google executive Ross LaJeunesse of Biddeford. Green activist Lisa Savage of Solon and independent Danielle VanHelsing of Sangerville have also filed to run.