The latest poll of the U.S. Senate race in Maine, released Friday by Colby College, shows Democrat Sara Gideon maintaining a narrow lead over incumbent Republican Susan Collins.

It also suggests neither candidate has a clear advantage with ranked-choice voting.

In the presidential race, former Vice President Joe Biden held a sizable lead, with 50 percent of respondents saying they planned to vote for him and 39 percent favoring President Trump. That margin is similar to other public polls released this month.

In the survey of 847 likely voters conducted between Sept. 21-24, 45 percent of respondents said they planned to vote for Gideon while 41 percent favored Collins. Five percent said they supported Republican-turned-independent Max Linn, 3 percent picked Green Independent Lisa Savage and 6 percent were undecided. The poll’s margin of error was plus or minus 3.4 percentage points.

“Our findings show an exceedingly tight race, with very little movement,” said Dan Shea, chair of Colby’s Department of Government and the lead researcher on the project. “Our data suggests it’s probably a bit closer than some of the other recent polls have been predicting. The percentage of undecided voters has been cut in half, but Gideon and Collins have netted about the same number of those voters.”

Colby’s last poll of the race in July showed Gideon with a 44 percent to 39 percent advantage with 12 percent undecided. Neither Linn nor Savage was named in that poll, but 6 percent favored another candidate.

Other public polls out this month have showed Gideon with a similar lead, including a poll of 500 likely voters by Suffolk University and the Boston Globe that had Gideon with 46 percent support, Collins at 41 percent and Savage and Linn at 3.8 percent and 1.6 percent, respectively, with 5 percent undecided. A poll of 663 likely voters by the New York Times and Siena University found Gideon was ahead 49-44 percent, but that survey did not include the other candidates.

Colby’s poll this week also asked respondents who their second choice would be under Maine’s ranked-choice voting system. Both Gideon and Collins were the second choice for 8 percent of respondents.

Nicholas Jacobs, one of the Colby faculty members working on the poll, said two things stood out from asking about ranked-choice voting.

“First, a large number of Gideon and Collins supporters don’t report having a second choice, even when given the option,” he said. “Second, Gideon and Collins both pick up about the same number of supporters on the second round, so no clear pattern emerges. The race stays just as tight after the ranked-choice is factored in, so it will likely come down to how the remaining 6 percent of undecided voters ultimately cast their ballot.”

The poll also suggests that female voters favor Gideon over Collins with 46 percent saying they would select Gideon as their first choice compared to 38 percent for Collins.

The poll also surveyed a smaller sampling of voters on the issue of whether Collins should vote to fill the seat on the U.S. Supreme Court left vacant by the death of Justice Ruth Bader Ginsburg, or whether that vote should be left until after winner of the presidential election is sworn into office in 2021.

Collins has said the Senate should wait on that vote and 58 percent of the poll’s respondents agreed with her, including 52 percent in the state’s more rural and conservative 2nd Congressional District.

Shea said he was surprised that Collins’ numbers in that district, which includes her hometown of Caribou, were not stronger. Only 47 percent of respondents said they would pick Collins as their first choice compared to the 38 percent who said they favored Gideon.

“For any incumbent to be under 50 percent in their home base, that’s a flashing red light for her campaign,” Shea said.

In the 2nd District, Biden’s lead shrank to 3 points (46 percent to 43 percent) among those polled. Maine is one of two states (along with Nebraska) that apportions electoral college votes by congressional district. One vote is awarded to the winner of each district and two are awarded to the winner of the state overall. In 2016, Trump lost to Democrat Hillary Clinton in the 1st District and statewide but carried the 2nd District and its one electoral vote.

“It’s certainly not a surprise that the president’s team is investing in the 2nd (district),” said Shea, referring to recent visits by Trump surrogates, including his sons, Eric and Don Jr. “There are a number of scenarios where one electoral vote could decide the presidency. Here again, it’s going to be a nail-biter.”

Although the presidential race is close in the 2nd Congressional District, 1st term Congressman Jared Golden, a Democrat, holds a big advantage over Republican challenger Dale Crafts. Of those polled, 56 percent said they will vote for Golden, 33 percent picked Crafts and 11 percent were undecided.

Finally, 58 percent of respondents said they planned to vote in person on Election Day and 36 percent would vote absentee by mail. Six percent were undecided. Asked if they felt that the election process in Maine would be fair and safe, 80 percent said they were “very” or “somewhat” sure. However, when asked the same question about the security of election nationwide, the figure dropped to 54 percent.