Democrats have yearned for a moment of political exoneration ever since Hillary Clinton’s defeat in 2016. They have looked to Russian interference in the campaign, claims of bias in the media and allegations of Republican lawbreaking to explain an upset that few in the party foresaw.

Perhaps most of all, Democrats have vented indignation at the FBI and its former director, James B. Comey, for reviving the issue of Hillary Clinton’s private email server in the last days of the race.

On Thursday, Clinton supporters won a powerful kind of validation from the unlikeliest source: President Donald Trump’s Justice Department.

The inspector general’s report criticising Mr Comey for his flamboyant handling of the Clinton investigation sent an angry thrill through the ranks of Democrats and Ms Clinton’s allies.

Michael E. Horowitz, an investigator not appointed by Mr Trump, concluded that Mr Comey had twice breached the bureau’s traditional discretion: first by holding a July 2016 news conference to announce he would not charge Ms Clinton with mishandling classified information, and then later sending a letter to Congress disclosing that the agents were scrutinising new evidence in the matter.

In many respects, those findings mirrored Democrats’ own assessments of Mr Comey – save for the omission of certain four-letter words.

But if the report appeared to validate their grievances against Mr Comey, it offered scant relief to Clinton loyalists. For some of them, it intensified the agony of Mr Trump’s surprise win – cementing Democratic suspicions about the fairness of his election, but leaving them without recourse to address them.

“Reading this report clearly makes me sick,” said Donna Brazile, who was chairwoman of the Democratic National Committee during the 2016 general election. “It confirms what we all believed at the time.”

The report, Ms Brazile said, strengthened her view “that 2016 will always be an election where there’s an asterisk.”

Randi Weingarten, president of the American Federation of Teachers and a longtime Clinton ally, said the report showed there had been a “double standard” in the election, whereby the FBI revealed information casting Ms Clinton in an unflattering light while concealing investigations into Mr Trump.

“It’s disappointing and infuriating,” Ms Weingarten said. “There is a reason for these norms of not commenting, knowing full well that comments can sway public opinion.”

While Ms Weingarten called the inspector general’s report a “service to the country,” she said it brought no solace on a personal level. “There’s no sense of vindication for one reason: look who’s in the White House right now,” she said.

And Robby Mook, Ms Clinton’s former campaign manager, said in an email that the report was concerning for reasons beyond Mr Comey’s “bad judgment.”

James Comey says Donald Trump was 'just making stuff up' about him breaking the law over releasing memos

It also documented the perception, within the bureau, that Mr Comey sent his October letter in part because he feared word of the investigation would leak – something Mr Mook said happened in other instances, to Ms Clinton’s detriment.

“There was a steady stream of leaks about the Clinton investigation for months but not a word about the counterintelligence probe into the Trump campaign,” Mr Mook said. “This, too, gave voters a false impression. I hope this report is a source of introspection for the professionals at the FBI.”

Mr Comey’s status as a Democratic bête noire is nearly two years old, dating to his news conference on 5 July, 2016, that the inspector general described as “extraordinary and insubordinate.”

But it was his letter to Congress nearly two weeks before the 2016 election – termed a “serious error in judgment” by the inspector general – that transformed him, for Democrats, into a starring villain of the presidential campaign.

Ms Clinton offered only a laconic public reaction on Thursday to the inspector general’s report, highlighting on Twitter a finding that Mr Comey had at times used a personal email account to conduct official business. “But my emails,” she tweeted, invoking a phrase often used by her supporters to express exasperation about what they view as the mistreatment of Ms Clinton during the election.

She has been more expressive about Mr Comey at other times. Within days of her loss, she named the FBI director as a key culprit: she told donors on a phone call that Mr Comey’s letter had “stopped our momentum” at the race’s end. At a public event in May 2017, she identified Mr Comey’s announcement as a turning point: “If the election had been on Oct. 27,” she said, “I would be your president.” (Mr Comey sent his letter on 28 October, 2016.)

Ms Clinton’s campaign strategists have long been convinced that the Comey letter changed the direction of the race, burying her closing message and helping Mr Trump reverse the fracturing of his support on the right after the release of the “Access Hollywood” tape. In the absence of a furore like the one instigated by Mr Comey, the publication of a recording that showed Mr Trump boasting about grabbing women’s genitalia could well have been the defining event of the campaign.

Experts differ on whether public opinion data suggests Mr Comey’s letter tipped the election. An analysis by the American Association of Public Opinion Research found “at best mixed evidence” to support the claim that Mr Comey’s letter was decisive. The study found that Mr Comey’s letter had “an immediate, negative impact” for Ms Clinton but questioned whether that effect lasted through Election Day.

But there is no question that Mr Comey’s choices had an effect on the campaign: His summer news conference and his missive to Congress plainly amplified the issue of Ms Clinton’s email server and her handling of classified information. Mr Trump seized on both events, citing the first in countless denunciations of the Obama administration – which he accused of going easy on his Democratic opponent – and wielding the second as a cudgel in the campaign’s final days.

In addition to chiding Mr Comey for sending that letter, the Justice Department report also concluded that there was no evidence of political bias in the FBI’s treatment of Ms Clinton, puncturing Mr Trump’s claim of favouritism.

Steve Elmendorf, a Democratic lobbyist who helped raise money for Ms Clinton’s campaign, said the inspector general’s report reinforced Democrats’ view of how the FBI handled the election. He said Mr Comey’s subsequent clashes with Mr Trump and firing had complicated Democrats’ judgments of the former bureau director but said nothing could “forgive the original sin of impacting the election.”

And the report, Mr Elmendorf added, was no salve for the wounds of 2016.

“People are so deep in all the other terrible things Trump has done,” he said. “There is no psychic relief from what happened, other than winning the next election.”