EXCLUSIVE: Former CIA Director John Brennan says the biggest threat to the 2020 election is Trump himself

• Former CIA Director John Brennan told Insider that the biggest threat to the November election is President Donald Trump himself.
• He said the "dishonesty" and disinformation that come out of the White House and Trump campaign are just as dangerous as foreign interference in the election.
• Brennan has earned a reputation as one of Trump's most vociferous critics since he left the CIA in 2017, and he doesn't mince words in his new memoir, "Undaunted: My Fight Against America's Enemies, at Home and Abroad."
• The former CIA chief wrote that he was "disgusted" and "nauseated" by Trump's behavior toward the US intelligence community and his refusal to acknowledge Moscow's campaign to interfere in the 2016 election.
• Overall, Brennan told Insider, Russia got everything it could have hoped for from Trump's presidency.

Former CIA Director John Brennan believes the biggest threat to the 2020 election is the sitting US president.

"Dishonesty, especially that coming out of the Donald Trump campaign, and the fact that you have certain networks that continue to misrepresent the facts in a very willful and dishonest fashion, is the main risk," he told Insider in an interview. "Trump has a very well established and recognized track record of misrepresenting the truth, and he will continue to do so. And unfortunately, there are too many people who just drink in that demagogic rhetoric that he spews out."

Brennan spent more than two decades at the CIA and served as director of the agency from 2013 to 2017. Before that, he worked as an analyst in the Near East and South Asia division and later as a station chief in Saudi Arabia and head of the National Counterterrorism Center.

Brennan left public service in 2005 to work in private-security consulting, but he returned to the government in 2009. In 2013, then-President Barack Obama nominated Brennan to lead the CIA, which he did until 2017.

Since leaving the US government, Brennan has developed a reputation as one of Trump's sharpest and most consistent critics. But Brennan's concerns about the president took root long before he departed his post as CIA director, according to his new book, "Undaunted: My Fight Against America's Enemies, at Home and Abroad," which was released on Tuesday.

The book opens with a fraught scene that took place on January 6, 2017, days before Brennan left the agency. He and other US intelligence chiefs briefed Congress' "Gang of Eight" and, later, then-President-elect Donald Trump about Russia's unprecedented and elaborate interference in the 2016 election. The attack, and Trump's refusal to acknowledge it, would become one of the defining parts of his presidency.

During the briefing, Brennan wrote, Trump repeatedly cast doubt on the veracity of the intelligence, despite the fact that the heads of the CIA, National Security Agency, FBI, and the director of national intelligence agreed on its contents.

Near the end of the briefing, Trump suggested that intelligence provided by human sources could be fabricated for personal gain.

"Anyone will say anything if you pay them enough. I know that, and you know that," Trump told Brennan, the book said.

The former CIA director wrote that he was "disgusted" by the president-elect's comments, given the life-threatening circumstances human intelligence sources place themselves in to serve their country.

"I stared at Trump" and "bit my tongue nearly hard enough to draw blood," Brennan wrote. "I knew that he saw me at the time not as John Brennan the person but as the director of the CIA, and I did not want to irredeemably spoil the CIA's relationship with the incoming president before it even got started."

As the briefing ended, Brennan wrote that he became "even more convinced that my long-held assessment of Trump's narcissism, lack of principles, and unfitness for the country's highest office was accurate. He showed no intellectual curiosity about what Russia had done and how it had carried out its campaign to interfere in the election, which suggested to me that he wasn't interested in learning the truth or in taking action to prevent a recurrence."

Nearly four years later, the former CIA chief's assessment hasn't changed. And fewer than 30 days out from November 3, Brennan said the disinformation flowing out of the White House and its allies in the conservative media is just as dangerous as foreign disinformation.

"There is an overlap between the two because a fair amount of what's happening here, whether it's coming out of domestic sources, is being fueled and encouraged by foreign actors," Brennan told Insider. "When I look at the polarization of our society and the rise of the far right and far left, a lot of that has domestic foundations, but our foreign adversaries want to stoke those fires to further enrage the social discourse, to make people on both ends of the spectrum more radical and more extremist."

CIA employees feel 'demoralized' under Trump and have 'deep concern' about the politicization of intelligence, Brennan says

Further hobbling the US is the politicization, manipulation, and suppression of intelligence that's taken place under the Trump administration.

Last month, a former senior Department of Homeland Security official, Brian Murphy, filed a whistleblower complaint saying he was told to stop focusing on Russian election interference and withhold intelligence assessments about the matter because it made the president "look bad."

In August, Director of National Intelligence John Ratcliffe announced he would no longer brief Congress on foreign election interference, though he partially reversed course in mid-September, saying his office would resume briefings for the House and Senate intelligence committees.

And last week, Ratcliffe again made headlines when he sent a letter to Senate Judiciary Committee Chairman Lindsey Graham revealing dubious information from a "Russian intelligence analysis" claiming that Hillary Clinton "approved a campaign plan to stir up a scandal" against Trump in 2016 "by tying him to Putin and the Russians' hacking of the Democratic National Committee."

Ratcliffe declassified the information despite the fact that the US intelligence community "does not know the accuracy of this allegation or the extent to which the Russian intelligence analysis may reflect exaggeration or fabrication," according to the letter.

Ratcliffe and his predecessor, former acting Director of National Intelligence Richard Grenell, "badly abused their oath of office and responsibilities to this country," Brennan said. Ratcliffe's decision to send the letter was "a very selective release of information that was designed to promote the interests, objectives, and goals of Donald Trump. So it was very disappointing."

He also pointed out Ratcliffe's reputation as one of Trump's biggest attack dogs on Capitol Hill before he took over as head of the intelligence community. Indeed, Trump nominated the former Texas congressman for the DNI post after Ratcliffe berated and attacked the special counsel Robert Mueller last year over his findings in the FBI's investigation into Russia's interference in the 2016 election.

"He was a very partisan supporter of Donald Trump when he was in Congress," Brennan said of Ratcliffe. "And he's just continuing to play that role as director of national intelligence."

The ex-CIA director said many of his former colleagues at the agency have found Trump's tightening grip on the intelligence community "demoralizing" and expressed "deep concern about what they see happening" in the national security apparatus.

"They see that their intelligence is not being used to further US interests, it's being disregarded and dismissed by the chief executive. And that leads a lot of my former colleagues to question why they continue to work so hard if their efforts are not being useful and worthwhile," he said. "So this has a very deleterious effect on the workforce."

A 'weaker' US under Trump is Putin's gain

Brennan, for his part, wrote that he became aware of Trump's transactional and political approach to leading the intelligence community from his very first day on the job.

On January 21, 2017, one day after being inaugurated as the commander in chief, Trump visited the CIA's headquarters in Langley, Virginia. While standing in front of the Memorial Wall, which pays tribute to every CIA officer who died in the line of duty, Trump boasted about the crowd size at his inauguration, while Brennan watched the event on television.

"I couldn't take it anymore. I felt physically nauseated watching and listening to him," Brennan wrote in his book. He went to the gym to work off his anger. That was the first time he publicly spoke out against the president, texting his former chief of staff, Nick Shapiro, the following statement: "Former Director Brennan is deeply saddened and angered at Donald Trump's despicable display of self-aggrandizement in front of CIA's Memorial Wall of agency heroes. He should be ashamed of himself."

As for how Trump has fared since then, Brennan did not mince words, saying the president is the biggest threat to the US's national security and future. Russia, on the other hand, got everything it could have hoped for from the Trump presidency, he said.

"The weaker the United States is, and the more tarnished our reputation is in the eyes of the world, the less able we are to play the leadership role we've played over the last 75 years," he said. "So what's happened to the US now plays directly into Putin's goals."