Updated| James Clapper, the former director of national intelligence, has spoken out about Russia's bid to subvert the 2016 presidential election.
In his new memoir, Facts and Fears: Hard Truths From a Life in Intelligence, Clapper describes evidence that Russian President Vladimir Putin swayed the election in a bid to secure Trump's election as "staggering."
"Of course, the Russian efforts affected the outcome," writes Clapper, as cited in a Washington Post review.
"Surprising even themselves, they swung the election to a Trump win. To conclude otherwise stretches logic, common sense and credulity to the breaking point. Less than eighty thousand votes in three key states swung the election. I have no doubt that more votes than that were influenced by this massive effort by the Russians."
Describing a report on Russian interference presented by the intelligence community to president-elect Trump in January 2017, Clapper writes, "I remember just how staggering the assessment felt the first time I read it through from start to finish, and just how specific our conclusions and evidence were."
In the intelligence chief's view, "We showed unambiguously that Putin had ordered the campaign to influence the election…and how the entire operation had begun with attempts to undermine U.S. democracy and demean Secretary Clinton, then shifted to promoting Mr. Trump when Russia assessed he was a viable candidate who would serve their strategic goals."
Clapper warns of the threat posed by Trump's dismissal of inconvenient facts as "fake news."
"I don't believe our democracy can function for long on lies, particularly when inconvenient and difficult facts spoken by the practitioners of truth are dismissed as 'fake news,' " Clapper writes. "I know that the Intelligence Community cannot serve our nation if facts are negotiable."
Clapper does not go so far as to state that Trump colluded with Russia, but he describes the president's attitude in face of evidence of Russian interference as one of "aggressive indifference."
Trump has strenuously denied allegations of colluding with Russia, describing investigations into the claims as a "witch hunt."
Clapper is also critical of Republican congressional leaders for refusing to sign a bipartisan statement condemning Russian meddling in 2016.
"House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell said they would not support a bipartisan statement that might hurt their nominee for president," Clapper writes in an excerpt of the book published by NPR. "I was disappointed but not surprised. It seemed they had decided by then that they didn't care who their nominee was, how he got elected or what effects having a foreign power influence our election would have on the nation, as long as they won."
A spokeswoman for Ryan and McConnell denied Clapper's claims, and in a stament to Newsweek said "Mr. Clapper has his facts wrong. What was discussed with the White House staff in September was a letter to the states warning against attacks during the election, which was quickly drafted and sent on September 28th."
Clapper has emerged as one of the fiercest critics of Trump among former leaders of the intelligence community since resigning in November, 2016.
On Tuesday, he criticized the president for demanding the Justice Department investigate allegations that the FBI placed a mole in the Trump campaign.
"When the president—this president or any president—tries to use the Department of Justice as kind of a private investigatory body, that's not good for the country," Clapper told CNN.
* This article was updated on May 24 with a statement from congressional Republican leaders Mitch McConnell and Paul Ryan.