A new poll shows Democrat Sara Gideon with a 12 percentage-point advantage over Republican Sen. Susan Collins in a head-to-head match-up. However, the poll failed to survey participants about two independents on the ballot.

The survey by Quinnipiac University Poll showed Gideon leading Collins 54 percent to 42 percent, with 89 percent of respondents saying their minds were made up on the race.

The university surveyed nearly 1,200 likely Maine voters Sept. 10-14, a period that coincided with a steady barrage of post-Labor Day advertising, as well as the first televised debate between Collins, Gideon and independents Lisa Savage and Max Linn.

But the Quinnipiac pollsters did not include Linn or Savage, despite their names being on the ballot and Maine’s use of ranked-choice voting in congressional elections. Instead, pollsters asked participants to choose Gideon and Collins “if the election for United States Senator were being held today.”

Just 1 percent of respondents replied, without prompting, that they supported someone other than the two, with 3 percent undecided. The survey had a margin of error of plus or minus 2.9 percent. The full list of questions and a breakdown of responses is below.

Numerous recent polls have shown Gideon leading Collins in a race that is drawing national attention and money because control of the U.S. Senate is potentially at stake in 2020. But the Quinnipiac poll shows Gideon – a Freeport resident currently serving as speaker of the House in the Maine Legislature – with her largest margin to date.

A statewide poll released last week by AARP Maine showed the Senate race as a statistical dead heat, with Gideon leading Collins 48 percent to 47 percent. That gap remained the same even when Savage was included and picked up 6 percent.

A survey in early August of 500 likely voters by Digital Research/Critical Insights for the Bangor Daily News had Gideon up 5 points over Collins, which is the same margin as a late-July poll of nearly 900 likely voters conducted by Colby College.

Political analysts will be closely watching to see what role, if any, ranked-choice voting plays in Maine’s elections.

Under the system, voters have the option of ranking candidates in their order of preference on the ballot. If no candidate receives more than 50 percent on the first tally, the candidate at the bottom is eliminated and their supporters’ votes are given to whoever those voters marked as their second choice. That process continues until one candidate wins the majority of the remaining vote pool.

Savage and Linn are long shots for winning the seat given their lower name recognition and the fact that more than $60 million has been spent to date by Gideon, Collins and outside groups. But the two independents could keep the front-runners from initially winning a majority, thereby triggering a ranked-choice runoff.

When asked about why Savage and Linn were left out, Quinnipiac University polling analyst Mary Snow said the program’s lead pollster has found that third-party candidates often perform better in surveys than they do at the ballot box.

Self-identified independents favored Gideon 59 percent to 36 percent – a ratio that, if accurate, would bode poorly for Collins because Democrats (the largest voting block in Maine) supported Gideon 93 percent to 6 percent. Additionally, women overall favored Gideon 58 percent to 38 percent.

“There are still debates to be had and a lot can happen between now and November 3, so this is just a snapshot in time,” Snow said. “But that’s what we are finding.”

Quinnipiac’s poll also showed former Vice President Joe Biden with a wide lead over President Trump, 59 percent to 38 percent. While Republicans and Democrats predominantly aligned with their party’s candidate, self-identified independents favored Biden 65 percent to 30 percent.

The survey even showed Biden leading Trump 53 percent to 44 percent in Maine’s more conservative 2nd Congressional District. Trump won the 2nd District in 2016, earning him one of Maine’s four presidential electors.

While the plurality of respondents (44 percent) said their views on Trump would have no impact on their vote in the Senate race, Snow said the survey indicates “there’s no ‘middle of the road’ when it comes to President Trump.” And that could affect support for Collins on Election Day, she said.

“When you take the poll as a whole, Donald Trump is very unpopular,” Snow said. “You see Biden with a 21-point lead, so that clearly is not helping Senator Collins.”