James Cook of Rockport, Maine, is a progressive voter who said he wants to see four-term incumbent Republican Sen. Susan Collins removed from the U.S. Senate.

But the 49-year-old activist and sociology professor is not voting for Collins' top competitor, Sara Gideon, as his No. 1 choice.

That’s because, Cook says, his state’s election system, ranked-choice voting, allows him to vote his conscience. He gave his No. 1 vote to his favorite candidate, independent Lisa Savage, and chose Gideon as his second choice. If Savage loses and neither Collins nor Gideon get a majority, his vote will go to Gideon.

“This allows me to have my cake and eat it, too,’’ Cook told GBH News on Monday. “I can make sure that I have a vote that goes to Sara Gideon, but I can also let her know that I'd like her to change her direction of policies a little bit.”

In 2016, Maine became the first state in the union to approve ranked-choice voting at the state level. A similar initiative is on the Massachusetts ballot, as Question 2.

Left-leaning Mainers hope the voting initiative will help Gideon give Democrats control of the U.S. Senate.

The competitive race has gained attention and millions of dollars from donors across the United States — including Massachusetts — making it the most expensive race in Maine’s history. Recent polls, including one from Colby College, finds the candidates running neck and neck.

It’s likely a decision won’t be available soon. Amy Fried, a political science professor at the University of Maine, says if neither Senate candidate wins a majority, it could take a week or longer for all votes to be tallied.

There’s also a possibility that if Collins loses, the Republican Party could file a lawsuit to fight the process. Other lawsuits, however, have not been successful.

Lyn Donovan of the seaside town of Camden says she too voted for Savage as her top choice, with Gideon as her second. "I think if we have any hope at all of dumping Susan Collins, she's the one who's going to carry it,’’ she said about Gideon.

Donovan said she’s not happy about the out-of-state monies heading into Maine — even if much of the money is supporting her candidate.

“It speaks to a national agenda, not a state agenda. And I think our senators and representatives need to be in Congress truly representing the needs of the state,’’ she said. “I think it is just wrong.’’

Political activist Karin Leuthy says she doesn’t begrudge the money coming in from out of state. But in the end, only Mainers can vote.

Leuthy is founder of the nonprofit volunteer group Suit Up Maine, a left-leaning group founded in 2016 to raise awareness and promote what she calls progressive ideals. On Monday, Leuthy headed out to knock on more doors.

“We have our hands full,’’ she said. “The balance of the Senate could very well hinge on Maine.”