President Donald Trump's former campaign chairman, Paul Manafort, suggested as early as the summer of 2016 that Ukrainians might have been responsible for hacking the Democratic National Committee during the presidential campaign rather than Russians, a key witness told federal investigators last year.

Newly released documents show that Manafort's protege, deputy campaign manager Rick Gates, told the FBI of Manafort's theory during interviews conducted as part of former special counsel Robert Mueller III's investigation of Russian interference in the 2016 presidential campaign. Gates told the FBI that Manafort had shared his theory of Ukrainian culpability with him and other campaign aides before the election.

The new information shows how early people in Trump's orbit were pushing the unsubstantiated theory about Ukraine's role. And it illustrates a link between Mueller's investigation, which concluded in March, and the current House impeachment investigation of Trump. The president had pushed Ukrainians to open a probe into whether their country interfered in the election - an assertion his allies have made in an effort to discredit Mueller's findings about Russia's role.

The documents were released in response to a lawsuit filed by BuzzFeed seeking documents related to Mueller's investigation. The news organization on Saturday, Nov. 3, published the first installment of internal Mueller records, released by the Justice Department to BuzzFeed in response to a court order.

They include heavily redacted summaries of interviews the FBI conducted during the investigation with Gates, as well as with former Trump lawyer Michael Cohen and former senior adviser Stephen Bannon, along with other documents.

The documents show that Gates told the FBI that Trump adviser Michael Flynn had been "adamant" that the Russians were not responsible for the hacking.

Flynn, who served briefly as Trump's first national security adviser, pleaded guilty in 2017 to lying to the FBI about his contacts with the Russian ambassador. This month, his lawyers suggested that he had not intended to lie and was instead entrapped by the FBI.

Sidney Powell, an attorney for Flynn, on Saturday called Gates' statement regarding Flynn "hogwash."

The documents also help explain why Mueller and his team spent months investigating the possibility that Donald Trump's campaign may have had advanced knowledge of releases of emails stolen allegedly by Russia and released publicly by WikiLeaks.

Interview summaries show that Gates told the FBI of various moments that led him to believe that Trump and others might have learned of WikiLeaks' plans ahead of time. An attorney for Gates, who has been cooperating with prosecutors since pleading guilty in February 2018 to conspiracy and lying to the FBI, did not respond to a request for comment on Saturday.

Ultimately, Mueller did not charge anyone associated with Trump's campaign of working with Russia or WikiLeaks to release stolen information, and Mueller's 448-page report did not accuse anyone of having advanced knowledge of WikiLeaks' plans.

Regarding Ukraine, a summary of an interview with Gates conducted in April 2018 shows that Gates told the FBI that Manafort citing Ukrainians for the hacks "parroted a narrative" that was also advanced at the time by Konstantin Kilimnik - an employee of Manafort who the FBI has assessed to have ties to Russian intelligence.

Trump and some of his allies have long pursued a theory that perhaps Ukraine had a hand in interfering with the 2016 election. Witnesses testifying before the House impeachment inquiry have indicated that they believe Trump conditioned military aid to Ukraine on that nation's new president agreeing to open an investigation into its role in the 2016 election as well as an inquiry of Trump's domestic political rivals.

In a July 25 phone call, Trump personally urged Ukraine's president Volodymyr Zelensky to investigate the matter.

The theory would serve to undermine any suggestion that Trump needed Russian assistance to win the election - and exonerate Russia for its role. The U.S. intelligence community has indicated it has a high degree of confidence that it was Russia and not Ukraine or any other country that was to blame for the hacking. In July 2018, Mueller's prosecutors indicted 12 Russian military officers and accused them of orchestrating the hacks.

Gates' comments suggested that the theory that Ukraine was to blame for the hacks may have originated with Kilimnik, a Russian employee of Manafort's political consulting operation in Kyiv.

Kilimnik was charged with tampering with witnesses in the Mueller investigation. He is believed to be in Moscow. He has denied ties to Russian intelligence and did not respond to a request for comment on Saturday. Gates told the FBI that Kilimnik had also suggested that the hacks could have been conducted by Russian operatives working out of Ukraine.

The newly released documents show that Gates also told the FBI that Trump's campaign was euphoric after WikiLeaks began publishing the hacked emails in July 2016, on the eve of the Democratic National Convention, and eager to put them to use to help the election bid. He testified that he believed the Republican National Committee appeared to have advanced knowledge of the timing of email releases through WikiLeaks. A spokesmen for the RNC did not immediately return a request for comment.

Shortly after the Democratic convention, Gates told the FBI that he was traveling in a car with Trump to the airport from Trump Tower in New York when Trump received a phone call related to WikiLeaks. Shortly after boarding an airplane, Gates said, Trump informed him that additional releases of information would be forthcoming.

Indeed, in October 2016, WikiLeaks released thousands of emails stolen from the account of John Podesta, the campaign chairman for Democratic nominee Hillary Clinton.

In written answers to questions posed by Mueller, Trump indicated he had no advanced knowledge of WikiLeaks' plans. At the time, Trump confidant Roger Stone was bragging publicly and privately that he had information about WikiLeaks' plans. He has since said his boasts were exaggerated and he was not in contact with WikiLeaks.

Stone goes on trial next week in Washington, accused of lying to Congress about his efforts to learn WikiLeaks' plans.

As the Trump campaign scrambled to learn what WikiLeaks held, Gates told the FBI that he could remember a moment on the campaign plane when candidate Trump ordered his subordinates: "Get the emails." Flynn responded that he could use his "intelligence sources" to try to obtain copies of the stolen emails in WikiLeaks possession.

The documents show that the Trump campaign struggled at times to decide how to respond to the growing evidence that Russia was interfering with the election.

As reports of the Russian effort mounted leading to Election Day, Erik Prince, a military contractor and informal adviser to Trump's campaign, emailed Bannon suggesting that the campaign create "an alternative narrative" about Russia's efforts - and that the Kremlin wanted Clinton, and not Trump, to win.

"Consider this response," Prince wrote in the October 2016 email released on Saturday. "It's unclear to me if Russia is directly involved in attempting to influence the US election. That said, its safe to say they are keenly interested, and likely using surrogates to poke in the US election. Who does the Kremlin want to see in the White House? Ms. Clinton."

Indeed, Trump has adopted the line repeatedly since his 2016 victory.

"You look at all of the different things, Russia would've much rather had Hillary than Donald Trump. I can tell you that right now," Trump told Fox News' Sean Hannity in March, at the conclusion of Mueller's investigation.

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This article was written by Rosalind S. Helderman and Spencer S. Hsu, reporters for The Washington Post.

The Washington Post's Devlin Barrett, Carol D. Leonnig, Tom Hamburger and Colby Itkowitz contributed to this report.