Former Director of National Intelligence James Clapper, whose five-decade career in intelligence has spanned Republican and Democratic administrations, said his decision to break with convention and speak out about the Trump administration stems from a concern about the institutional integrity of the country.

"It's [in] my very being to want to support the President of the United States, particularly in his role as Commander-in-Chief," said Clapper, who served as President Obama's intelligence chief from 2010 to 2017. "This president makes that very difficult because I feel that our institutions and values are under assault both from an external source – the Russians – and from an internal source – our own president."

"This is a real test of our resilience as a country, as a system of governance – it is a real test," he said.

In an interview with "Intelligence Matters" host and CBS News Senior National Security contributor Michael Morell, Clapper said he and President-elect Trump "got off to a bad start" after he and other senior officials briefed Trump on the findings of the Intelligence Community Assessment on Russian interference in the 2016 election. "He, five days later, referred to us in a press conference as 'Nazis,'" Clapper recounted, "and I felt I needed to speak up on behalf of the great men and women of the intelligence community."

Clapper has been the subject of several tweets by President Trump, mainly related to Special Counsel Robert Mueller's ongoing investigation into connections between Russia and the Trump campaign.

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"When James Clapper himself, and virtually everyone else with knowledge of the witch hunt, says there is no collusion, when does it end?" the president tweeted last month.

"I don't allege collusion, don't know that," Clapper told Morell, but says he observed a "striking parallelism" between some of the words and actions of Russians and Trump campaign members. "The parallelism was such that they were almost an echo chamber, particularly when it came to Hillary Clinton – describing her alleged scandals and her alleged maladies, both physical and mental," he said.

At least some of the Russians' brazenness stemmed from the insufficient costs imposed by the Obama administration, Clapper conceded, saying he expected the sanctions and expulsions taken by the Obama administration in late December to constitute "Phase One," and to be followed up accordingly. "In the 'coulda, woulda, shoulda' department," he said, "I wish we had done that earlier and that we had actually caused more pain for the Russians than we did."

He also acknowledged that the October 2017 statement he issued with Secretary of Homeland Security Jeh Johnson about Russian meddling failed to mention their widespread activity on American social media platforms. "And I don't have a good reason for that," he said, noting the decision to issue a statement at all came after a protracted political calculus.

Clapper elaborated on one of the central conclusions of his new book, "Facts and Fears: Hard Truths from a Life in Intelligence," in which he offered what he calls an "informed perspective" on the effect of Russia's election meddling.

"Based on pretty good understanding of the magnitude of what the Russians did, how massive it was, it touched probably 127 million voters," he said. "And in fact, that the election turned on fairly narrow margin 80,000 votes or so in 3 states."

"To me it stretches logic and credulity to think that that massive effort didn't affect the outcome of the election, given how closely decided it really was," he told Morell, and reiterated the intelligence community's widely held expectation that Russia will attempt to make similar incursions in this year's midterm elections and in 2020.

"I will say that in my 50-plus years in intelligence, I've seen a lot of bad things, but never anything that disturbed me as much as this," he said, "because this is a fundamental attack on the fundamental pillars of our political system."

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