American intelligence officials’ determination that Russia interfered in the 2016 presidential election to assist Donald J. Trump’s candidacy was fundamentally sound and untainted by politics, according to a key Republican-led Senate review released on Tuesday. The findings undercut longstanding allegations by Mr. Trump and his allies that the officials were biased against him.

The Senate Intelligence Committee, which conducted the three-year study, 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 on Tuesday presented new detail about the government’s attempts in 2016 and 2017 to make sense of Russia’s attacks. Much of the report’s contents about the so-called Intelligence Community Assessment were considered highly sensitive and blacked out by the Trump administration.

“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.”