An investigation into the origins of the FBI's probe into ties between Russia and Donald Trump's 2016 presidential campaign has finally been concluded, with the prosecutor leading the inquiry submitting a much-awaited report that found major flaws.

The report, the culmination of a four-year investigation into possible misconduct by U.S. government officials, contained withering criticism of the FBI but few significant revelations. Nonetheless, it will give fodder to Trump supporters who have long denounced the Russia investigation, as well as Trump opponents who say the Durham team's meager court record shows their probe was a politically motivated farce.

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A look at the investigation and the report:

WHO IS JOHN DURHAM?

Durham has spent decades as a Justice Department prosecutor, with past assignments including investigations into the FBI's cozy relationship with mobsters in Boston and the CIA's destruction of videotapes of its harsh interrogations of terrorism subjects.

He was appointed in 2019 to investigate potential misconduct by U.S. government officials as they examined Russian election interference in 2016 and whether there was any illegal coordination between the Kremlin and Trump's presidential campaign.

Despite skimpy results — one guilty plea and two acquittals — that failed to live up to Trump's expectations, Durham was able to continue his work well into the Biden administration, thanks in part to William Barr appointing Durham as a Justice Department special counsel shortly before Barr's 2020 resignation as attorney general.

WHY DID THE TRUMP JUSTICE DEPARTMENT THINK SUCH AN APPOINTMENT WAS NECESSARY?

The appointment came weeks after a different special counsel, Robert Mueller, wrapped up his investigation of possible connections between Russia and the Trump campaign. That probe produced more than two dozen criminal cases, including against a half-dozen Trump associates.

Though it did not charge any Trump aide with working with Russia to tip the election, it did find that Russia interfered on Trump's behalf and that the campaign welcomed, rather than discouraged, the help.

From the start, Barr was deeply skeptical of the investigation's foundation, telling Congress that “spying did occur” on the campaign.

He enlisted an outside prosecutor to hunt for potential misconduct at the government agencies who were involved in collecting intelligence and conducting the investigation, even flying with Durham to Italy to meet with officials there as part of the probe.

WERE THERE PROBLEMS WITH THE RUSSIA INVESTIGATION?

Yes, and a Justice Department inspector general inquiry already identified many.

The watchdog report found that FBI applications for warrants to eavesdrop on a former Trump campaign aide, Carter Page, contained significant errors and omitted information that would likely have weakened or undermined the premise of the application.

The cumulative effect of those errors, the report said, was to make it “appear that the information supporting probable cause was stronger than was actually the case.”

Still, the inspector general did not find evidence that investigators acted with political bias and said there was a legitimate basis to open a full investigation into potential collusion, though Durham has disagreed.

WHAT CRIMINAL CASES DID HE BRING AND WHAT WAS THE OUTCOME?

Durham brought three prosecution during his tenure, but only one resulted in a conviction — and that was for a case referred to him by the Justice Department inspector general. None of the three undid core findings by Mueller that Russia had interfered with the 2016 election in sweeping fashion.

A former FBI lawyer, Kevin Clinesmith, pleaded guilty in 2020 to altering an email related to the surveillance of ex-Trump campaign aide. He was given probation.

But two other cases, both involving alleged false statements to the FBI, resulted in acquittals by jury.

Michael Sussmann, a lawyer for the Hillary Clinton campaign, was found not guilty of lying to the FBI during a meeting in which he presented computer data information that he wanted the FBI to investigate. A different jury acquitted Igor Danchenko, a Russian-American analyst, of charges that he lied to the FBI about his role in the creation of a discredited dossier about Trump.

WHAT SPECIFICALLY DID DURHAM FIND?

Durham found that the FBI acted too hastily and relied on raw and unconfirmed intelligence when it opened the Trump-Russia investigation.

He said at the time the probe was opened, the FBI had no information about any actual contact between Trump associates and Russian intelligence officials.

He also claimed that FBI investigators fell prone to “confirmation bias,” repeatedly ignoring or rationalizing away information that could have undercut the premise of their investigation, and he noted that the FBI failed to corroborate a single substantive allegation from a dossier of research that it relied on during the course of the probe.

“An objective and honest assessment of these strands of information should have caused the FBI to question not only the predication for Crossfire Hurricane, but also to reflect on whether the FBI was being manipulated for political or other purposes,” the report said, using the FBI's code name for the Trump-Russia probe. “Unfortunately, it did not.”

HOW DID THE FBI RESPOND?

The FBI pointed out that it had long ago made dozens of corrective actions. Had those measures been in place in 2016, it says, the errors at the center of the report could have been prevented.

It also took pains to note that the conduct in the report took place before the current director, Christopher Wray, took the job in fall 2017.

WHAT HAPPENS NEXT?

It didn't take long for Republicans in Congress to react. Rep. Jim Jordan, who chairs the House Judiciary Committee, said he had invited Durham to testify on Capitol Hill next week. Trump, too, sought to seize on the report, claiming anew in a post on his Truth Social platform that the Durham report had found “the crime of the century” and calling the Russia investigation the “Democrat Hoax.”

Though the FBI says it's already taken some steps to address the problems cited in the report, Durham did say it's possible more reform could be needed. One idea, he said, would be to provide additional scrutiny of politically sensitive investigations by identifying an official who would be responsible for challenging the steps taken in a probe.

He said his team had considered but did not ultimately recommend steps that would curtail the FBI's investigative authorities, including its use of tools under the Foreign Intelligence Surveillance Act to eavesdrop on suspected spies or terrorists.