Democrat Sara Gideon (left) and Republican Sen. Susan Collins take their places at the Decision Maine debate in Portland on Sept. 11. Credit: (Brianna Soukup | Portland Press Herald

A Republican super PAC is making a late advertising push to support Sen. Susan Collins just after Democratic groups invested $10 million to boost challenger Sara Gideon in the final week of Maine’s competitive U.S. Senate race.

The Maine Way, a single-candidate super PAC supporting Collins, is spending $4 million, according to Advertising Analytics. The group, which has been dormant since its creation last year, looks to have received a last-minute cash infusion from an unknown source after having raised only $90,000 through Oct. 14, according to federal records.

It is affiliated with the Senate Leadership Fund, a super PAC aligned with Senate Majority Leader Mitch McConnell, R-Kentucky, that has already spent heavily to boost Collins. Its treasurer, Benjamin Ottenhoff, is the former chief financial officer of the Republican National Committee.

The new spending comes on top of more than $90 million that has already flown into the race from outside groups, as well as more than $71 million spent by candidates. Polling has been tight all year, with the most recent poll from Colby College, released Wednesday, giving Gideon a three-point edge, within the margin of error.

Outside spending in the race has slightly favored the Democratic challenger so far, led by spending by the Senate Majority PAC, a super PAC affiliated with Democratic Senate leadership, which has spent more than $22 million. Several groups affiliated with Republican leadership have spent to help Collins, including the Senate Leadership Fund as well as the National Republican Senatorial Committee and 1820 PAC.

The latest batch of spending comes as more than 417,000 Mainers have already successfully cast their ballots, according to state data, accounting for more than half of 2016 turnout. Democrats have greatly outpaced Republicans in absentee voting so far. The race, which also includes independents Lisa Savage and Max Linn, will use ranked-choice voting.