People leading Donald Trump's presidential campaign in 2016 either wittingly or unwittingly allowed themselves to be used by Russia in their bid to successfully elect the billionaire businessman U.S. president.

The U.S. Senate came to this conclusion in a 966-page report released this week concerning Russia's interference on Trump's behalf during the 2016 presidential election. The report found Russia "engaged in an aggressive, multifaceted effort to influence, or attempt to influence, the outcome of the 2016 presidential election."

The report said Russia was now working to repeat the operation to get Trump re-elected in November.

It said Russia's clandestine services, at the behest of President Vladimir Putin, successfully created a complex web of spies and active measures to ensnare members of Trump's campaign. This left the Trump administration open to later manipulation by Russia.

The report by the Senate Intelligence Committee said Paul Manafort, Trump's 2016 campaign chairman, posed a "grave counterintelligence threat" because of his dealings with people later proven to be spies for Russia.

"Manafort's presence on the campaign and proximity to Trump created opportunities for Russian intelligence services to exert influence...and acquire confidential information," the report said.

The report said Manafort had long-standing ties with Russia oligarch Oleg Deripaska and spy Konstantin Kilimnik. Deripaska, a billionaire, is known for carrying out influence operations on orders from the Kremlin.

The committee said it was especially bothered by Manafort's "close and lasting" relationship with Kilimnik. It said on numerous occasions Manafort secretly shared internal campaign information with Kilimnik. "The committee was unable to reliably determine why Manafort shared sensitive internal polling data or campaign strategy with Kilimnik or with whom Kilimnik further shared that information."

Manafort was convicted in 2018 of tax and bank fraud during a separate investigation by former special counsel Robert Mueller. He was released from prison to home confinement earlier this year because of the dangers of COVID-19.

Committee investigators said that, whether a result of ambition or naivety, important Trump campaign officials were indifferent to the possibility they were being assisted by Russia. The committee, however, didn't find conclusive evidence Trump campaign officials willingly and knowingly worked with Russia to win the election.

The report also criticized the Trump campaign's embrace of secret documents about the Democrats stolen and later made public by WikiLeaks. It said the Trump campaign "sought to maximize the impact of those leaks to aid Trump's electoral prospects."

"The Trump campaign publicly undermined the attribution of the hack-and-leak campaign to Russia and was indifferent to whether it and WikiLeaks were furthering a Russian election interference effort," the report said.

It also documented interaction between Trump associate Roger Stone and WikLleaks. It said WikiLeaks actively sought, and played, a big role in the Russia influence campaign and very likely knew it was assisting a Russian intelligence influence effort.

"Trump and senior campaign officials sought to obtain advance information about WikiLeaks's planned releases through Roger Stone," according to the report.

The committee's report is its fifth and last on the matter. It took both Senate Democrats and Republicans three years to compile and includes hundreds of witness interviews.