FULL VIDEO: Attorney General Bill Barr's press conference about the Mueller report

US Attorney General Bill Barr said Thursday that President Donald Trump took no action to thwart the special counsel's probe into Russian election interference, ahead of the long-awaited release of the final investigation report.

The politically charged case over whether or not Trump's campaign team colluded with Moscow -- and whether the president sought to derail that probe -- has captivated Washington for the better part of two years.

Special Counsel Robert Mueller, a former director of the FBI, was appointed to investigate the extent of Russian efforts to meddle in the 2016 presidential election and tilt it in Trump's favor.

He concluded that 22-month investigation in March, and Barr's summary of the report made public indicated he found no collusion. Barr reiterated those findings on Thursday.

"The special counsel's report states that his investigation did not establish that members of the Trump campaign conspired or coordinated with the Russian government in its election interference activities," the attorney general told reporters.

But the initial Mueller report summary left unanswered the question of whether Trump tried to obstruct the probe -- which is why Washington has breathlessly awaited its release.

Barr emphatically said Thursday that the Republican leader's actions -- including his public attacks on Mueller and firing of then FBI chief James Comey -- were not legally actionable.

Trump rejoiced after the press conference, tweeting "GAME OVER."

"There is substantial evidence to show that the president was frustrated and angered by a sincere belief that the investigation was undermining his presidency, propelled by his political opponents, and fueled by illegal leaks," Barr said ahead of the release of the Mueller report.

"Nonetheless, the White House fully cooperated with the special counsel's investigation, providing unfettered access to campaign and White House documents, directing senior aides to testify freely, and asserting no privilege claims," he said.

"And at the same time, the president took no act that in fact deprived the special counsel of the documents and witnesses necessary to complete his investigation," Barr said.

He revealed that Trump's lawyers were able to review the report earlier this week, adding that the White House made no changes to the wording.

- Democrats want Mueller to testify -

But Trump's Democratic opponents on Capitol Hill will be combing through the redacted 400-page report to see if any of the "10 episodes" of potential obstruction amount to grounds for impeachment.

House Judiciary Committee chief Jerry Nadler has asked that Mueller testify no later than May 23.

"It is clear Congress and the American people must hear from Special Counsel Robert Mueller in person to better understand his findings," Nadler tweeted.