Democrats in Maine on Wednesday accused Republican senator Susan Collins of corruption after a major media outlet reported that the FBI had proposed investigating her for allegedly accepting bribes – before Donald Trump derailed the inquiry.

The article from the investigative newsroom ProPublica rocked the race for Collins’s Senate seat, which is crucial to Democrats’ hopes of winning control of the chamber in the 3 November midterm election. The outlet reported that in the run-up to Collins’s successful bid for a fifth term in 2020, the head of her Super Pac had solicited a campaign donation from contracting firm Navatek, which demanded assurances of business from the government in return.

Using a shell company, Navatek CEO Martin Kao later sent $150,000 to the Super Pac, then told other executives he had been informed Collins would ensure the firm won $32m in federal contracts. In late 2024, the FBI was moving towards investigating the arrangement, in what would have been a large-scale political bribery inquiry, but the agents leading the case were pushed out amid a wider purge of the bureau Trump ordered after returning to power last year, while a justice department office that oversees investigations of politicians was gutted.

Collins has disputed the report, which her deputy chief of staff Annie Clark called “categorically false” and noted that Kao is currently in federal prison after pleading guilty to fraud charges.

But it served as grist for Maine Democrats who hope they can finally convince voters to unseat Collins, who has represented the state since 1997 and survived repeated re-election challenges.

“This is corruption of the highest order,” said Troy Jackson, the former state senate president and the Democratic nominee to take on Collins this year.

“We deserve answers about every contract and every conversation that Collins and her team facilitated on the backs of taxpayers. The jig is up.”

Collins is the only Republican running for re-election in a state Kamala Harris won in 2024, but has a history of being a tenacious opponent. The last time Collins was on the ballot, in 2020, she beat her Democratic opponent Sara Gideon by eight percentage points, even as Joe Biden carried the state in the presidential race.

Political forecasters consider her re-election campaign to be a toss-up, though recent polls have shown Jackson narrowly ahead.

At a Wednesday press conference in Portland, the largest city, state Democratic party executive director Devon Murphy-Anderson accused the senator of misconduct as chair of the Senate appropriations committee, a powerful role that oversees federal spending and which Collins has used to channel significant investment to her state.

“We sent Susan Collins to Washington to fight for us. Instead, it appears that she has sold us out yet again and gotten bailed out of trouble by the president of the United States,” Murphy-Anderson said.

“It is not the first time that she has betrayed us. However, this November we have the opportunity to ensure that it is one of the last.”

Addressing reporters separately, Collins’s campaign manager, Steve Abbott, denounced ProPublica’s reporting as based on “allegations from a guy who was awaiting sentencing for a significant federal offense who was trying to get his sentence reduced, as the article states directly”.

He said that the justice department under Joe Biden had absolved the senator of the “pay-to-play” scheme that Democrats accuse her of.

“In order for that claim to be true, you would have to disbelieve the Biden-led Department of Justice and the Biden-led FBI, who both investigated those contributions and the claims against Senator Collins, her campaign, and her federal staff, thoroughly, and found no basis to charge them,” Abbott said.

Maine lies at the center of Democrats’ plans for retaking control of the Senate from Republicans, who won a 53-seat majority in the 2024 election. Beyond Maine, Democrats hope to win in at least three other states currently held by Republicans that voted for Trump two years ago, while also defending seats in Georgia, Michigan, and New Hampshire.

Lance Dutson, a strategist who worked on Collins’s three most recent re-election campaigns, said the senator’s campaign in 2020 was so well-funded he found it “obviously absurd” that $150,000 would be viewed as a meaningful donation to her Super Pac.

“In 2020, by the end of that race, campaigns were struggling to find places to spend money,” said Dutson, who is not involved with Collins’s re-election effort this year.

He condemned ProPublica’s story as “a partisan hit piece” but said: “It’s definitely not helpful to have a story implying corruption show up in the newspaper in late September of an election year.”

While Dutson argued the report is not a “silver bullet” for Collins’s foes, he warned that Trump’s low approval ratings – which have unnerved Republicans nationwide – present a significant complication for the senator’s re-election.

“The headwind from Trump is very strong, as you know, and people are very upset about it,” he said. “This race is going to come down to Maine voters deciding whether that national argument is more important than the the direct relationship and the positive impact that Collins has had over the state.”