WASHINGTON — For years, President Trump has derided the assessment by American intelligence officials that Russia interfered in the 2016 presidential election to assist his candidacy, dismissing it without evidence as the work of a "deep state" out to undermine his victory.

But on Tuesday, a long-awaited Senate review led by members of Mr. Trump's own party effectively undercut those allegations. A three-year review by the Republican-led Senate Intelligence Committee unanimously found that the intelligence community assessment, pinning blame on Russia and outlining its goals to undercut American democracy, was fundamentally sound and untainted by politics.

"The I.C.A. reflects strong tradecraft, sound analytical reasoning and proper justification of disagreement in the one analytical line where it occurred," said Senator Richard M. Burr, Republican of North Carolina and the panel's chairman. "The committee found no reason to dispute the intelligence community's conclusions."

The endorsement by Mr. Burr's committee comes at a key moment for the intelligence agencies. Not only has Mr. Trump moved in recent months to install a loyalist in the top spy position, but Attorney General William P. Barr has also blessed a broad review of possible misconduct by investigators examining the Trump campaign's contacts with Russia, apparently including work by intelligence officials.

The federal prosecutor whom Mr. Barr appointed to review the government's response to Russian election interference, John H. Durham, is examining whether the C.I.A. or other intelligence agencies overstated President Vladimir V. Putin's support of the Trump campaign, a central finding of the 2017 assessment. His team has interviewed intelligence analysts, questioning whether Obama-era intelligence officials hid evidence or manipulated analysis about Moscow's covert operation, people familiar with the Durham inquiry have said.

Some of Mr. Trump's allies immediately criticized the Senate report; Fred Fleitz, a former C.I.A. officer who briefly served in the Trump administration, dismissed it as "a whitewash." Many Republicans believe that the intelligence agencies overstated Russia's support for Mr. Trump and argue that Moscow was trying to sow chaos in the United States, not support any one candidate.

Thursday's report was the latest installment in an inquiry by the Senate Intelligence Committee into the broader Russia matter. Senators are expected to release one final chapter in the coming months examining contacts between the Trump campaign and Russia.

When the inquiry began in early 2017, it was one of the most closely followed in the history of Congress, casting a cloud over Mr. Trump's presidency that could not be dismissed as merely partisan. But with the investigation into the same topic by the special counsel, Robert S. Mueller III, long since put to rest; an impeachment fight over a largely unrelated matter behind the country; and a pandemic reshaping nearly every aspect of life, the Russia inquiry has now largely become an afterthought for most Americans.

The Senate Intelligence Committee had already given the work of the C.I.A. and the F.B.I. an interim stamp of approval, but the 158-page report released on Tuesdaypresented new detail about the government's attempts in late 2016 and early 2017 to make sense of Russia's attacks. Much of the report's contents were considered highly sensitive and blacked out by the Trump administration before release.

In their report, senators essentially said they had asked the same questions that Mr. Durham is now examining and found that the intelligence agencies' work stood up, even if it was conducted in a compressed time frame to be finished before President Barack Obama left office in January 2017.

"The case is closed," said Senator Angus King, independent of Maine. "I don't know how you could have a much more credible source than a three-year study by a bipartisan committee that came to a unanimous conclusion."

Critics of the assessment have focused on the fact that the National Security Agency had a lower level of confidence than the C.I.A. and the F.B.I. on the conclusion that Mr. Putin supported Mr. Trump's election. Mr. Durham, they believe, can provide proof.

But the committee found that the differing confidence levels among the intelligence agencies were "justified and properly represented." The report said that both John O. Brennan, then the director of the C.I.A., and Adm. Michael S. Rogers, then the director of the National Security Agency, both "independently expressed to the committee that they reached the final wording openly and with sufficient exchanges of views."

Senators said their inquiry found that intelligence analysts who worked on the assessment were "under no politically motivated pressure to reach specific conclusions."

"All analysts expressed that they were free to debate, object to content and assess confidence levels, as is normal and proper for the analytic process," the report said.

It also examined the inclusion of material from a well-known dossier compiled by Christopher Steele, a former British intelligence officer whom the F.B.I. referred to by the code name "Crown," showing purported ties between the Trump campaign and Russia. The document included unverified, salacious accusations about Mr. Trump and has become a focus of Mr. Trump's allies, who have sought to conflate it with the much broader Justice Department investigation into Russia's election interference.

Though elements of the dossier were included in an annex to the intelligence assessment, it "was not used in the body of the I.C.A. or to support any of its analytic judgments," the senators found.

Even the decision to include it in the annex was made reluctantly, the senators wrote. The F.B.I. did not want to vouch for its veracity but felt that because Mr. Obama had ordered the assessment to include all relevant material, his directive required the dossier's inclusion.

The Senate report stood in contrast to the conclusions in 2018 of the House Intelligence Committee, then under Republican control, which took issue in its own report on Russian election interference with intelligence officials' conclusion that Mr. Putin had tried to harm Hillary Clinton and help Mr. Trump. The House committee cited breakdowns in "proper analytic tradecraft," but many House Republicans who were involved later disavowed that conclusion.

Earlier volumes released by the Senate committee chronicled Russia's active measures campaign to interfere in the 2016 election and outlined potential policy measures to blunt future attacks on election infrastructure, examined the use of social media to sow political divisions in the United States and critiqued the response by the Obama administration and Congress to Russia's attacks in the run-up to the last presidential election.

The committee is expected to release a final bipartisan installment in the coming months evaluating possible coordination between the Trump campaign and Russia. A draft runs over 900 pages but has yet to be submitted for classification review by intelligence agencies, a process that could take weeks or months.

The findings are likely to mirror those in the Mueller report. His team documented voluminous contacts between Russia and the Trump campaign, including a willingness by Mr. Trump's team to accept Russian assistance during the election, but concluded that it had insufficient evidence to charge any campaign official with conspiracy.

More recently, Mr. Burr, who slowly pushed his bipartisan investigation forward despite calls from Mr. Trump to disband it, has come under intense scrutiny for a decision to liquidate much of his stock portfolio in February, before the coronavirus pandemic ravaged the financial markets. The Securities and Exchange Commission and the Justice Department have taken preliminary steps to investigate whether the sales had been based on nonpublic information Mr. Burr received on the Intelligence Committee or through other Senate work, a potential violation of the law.

Mr. Burr noted that Russia had continued efforts to interfere in American politics, and he said the warnings of three years ago still must be heeded.

"Russia and its imitators increasingly use information warfare to sow societal chaos and discord," Mr. Burr said. "With the 2020 presidential election approaching, it's more important than ever that we remain vigilant against the threat of interference from hostile foreign actors."

Senator Mark Warner of Virginia, the committee's top Democrat, concurred and warned that Russia's success in 2016 would embolden the Kremlin to continue to interfere in American democracy.

Voices4America Post Script. As we face the Covid deaths & destruction exacerbated by Trump's evil & incompetence, we must not forget this. Even the GOP led Senate Intel Committee found Russia 🇷🇺 brought about the results of 2016. Russia gave us Trump. #TrumpIllegitimate #RememberInNov