Democratic challenger Sara Gideon leads by 5 percentage points over four-term Republican incumbent U.S. Sen. Susan Collins in a poll of nearly 900 likely Maine voters conducted by Colby College.

The survey, conducted between July 18-24 – not long after Gideon officially won the Democratic nomination – showed her with a 44 percent-39 percent advantage over Collins, with 12 percent undecided and 6 percent saying they planned to support another candidate.

Independent Tiffany Bond and Green Independent Lisa Savage, who will be on the ballot, were not named as options. The poll also did not ask about ranked-choice voting, which will be used in November.

Gideon’s lead is a slight increase from a poll done by Colby in February – shortly after President Trump was acquitted on his impeachment counts but before the coronavirus pandemic upended the country – that showed her with a narrow 43 percent-42 percent edge among registered voters.

“The number one factor that we find in our poll that predicts support for Collins or Gideon are attitudes about Trump,” said Dan Shea, professor of government at Colby and lead researcher on the poll. “That’s the anvil strapped around Sen. Collins’ back. As his numbers have declined, so have hers.”

In the presidential race, the Colby poll showed former Vice President Joe Biden leading Trump, 50 percent to 38 percent among Maine voters, with 7 percent undecided. The race was closer in the 2nd Congressional District, where Biden held a 45 percent-42 percent edge. Trump won Maine’s second district and its one electoral college vote four years ago.

In the 2nd Congressional District race between incumbent Democrat Jared Golden and Republican Dale Crafts, who won a three-way primary this month, 45 percent said they planned to vote for Golden, while 33 percent supported Crafts and 17 percent were undecided.

Shea said he was surprised to see an incumbent like Golden only poll at 46 percent and predicted that race to tighten as Crafts gains name recognition.

“We zeroed-in on likely voters instead of registered voters, and that’s important,” he said. “These are solid numbers for the Democrats, and the results are definitely good news for Gideon, Biden and Golden because polls of just registered voters can sometimes over-inflate Democratic turnout. At the same time, there are a ton of undecided voters, which is key for Collins and Crafts.”

Of the 888 voters surveyed, 31 percent were Democrats, 27 percent Republicans and 41 percent were unenrolled, which lines up with the percentage of each category registered in Maine. Of those polled, 300  were contacted through landlines or mobile phones, while 588 were reached online. The margin of error was 3.9 percentage points.

The 2020 race between Collins and Gideon is expected to be close and contentious. Already, both sides are spending record amounts of money on advertising and that’s likely to continue through the fall.

Republicans hold a six-seat advantage in the Senate, but Democrats are hopeful they can regain power and see Maine’s race as critical. Many other Republican senators who face re-election this year also are staring at closer-than-anticipated races.

Collins, 67, was first elected in 1996 and has been re-elected three times since, increasing her margin of victory each time. However, since Trump was elected in 2016, Collins’ popularity in Maine has waned, even more so after her 2018 vote to confirmed U.S. Supreme Court Justice Brett Kavanaugh.

Gideon, 48, is a four-term lawmaker from Freeport who has been Maine’s Speaker of the House since 2016.

Shea said the biggest surprise for him was low support for Collins among women.

“Only 27 percent of women under 50 say they’ll vote for Susan Collins (compared to 55 percent for Gideon). That’s an incredible number,” he said. “To me, that’s one of the key subgroup data points in the survey and its hard to imagine how the senator is re-elected unless that figure changes.”

Trump was viewed favorably by just 39 percent of those polled, while 59 percent viewed him unfavorably. The numbers for Maine Gov. Janet Mills were nearly the opposite, with 59 percent viewing her favorably and 35 percent unfavorably.

“With regard to Mills, that’s a really solid number and a validation for the governor that she’s handled the pandemic well,” Shea said. “I think any governor would take that approval rating in 2020.”

The poll also asked respondents a series of questions about the pandemic. An overwhelming majority (68 percent) said the government should establish clear rules on when and where face coverings should be worn.