James Clapper institutions assault President Trump sotu_00000000.jpg
James Clapper institutions assault President Trump sotu_00000000.jpg
Now playing
01:14
Clapper: US institutions under assault by Trump
PHOTO: CNN
Now playing
01:30
Ex-FBI agent 'disgusted' by Comey testimony
Joe Lieberman on EBOF 2
PHOTO: CNN
Joe Lieberman on EBOF 2
Now playing
01:25
Lieberman: Comey testimony serious allegations
PHOTO: Joe Raedle/MANDEL NGAN/AFP/Getty Images
Now playing
02:38
James Comey: Trump said he expected loyalty
James Comey FBI quad split
James Comey FBI quad split
Now playing
01:52
How James Comey is preparing for this moment
mobile panel reaction comey opening statement nr sot_00000706.jpg
mobile panel reaction comey opening statement nr sot_00000706.jpg
Now playing
00:26
Comey memos leave entire panel speechless
WASHINGTON, DC - MAY 21:  FBI Director James Comey testifies during a Senate Judiciary Committee hearing on Capitol Hill, May 21, 2014 in Washington, DC. The committee is hearing testimony on oversight of the Federal Bureau Of Investigation.  (Photo by Mark Wilson/Getty Images)
PHOTO: Mark Wilson/Getty Images/FILE
WASHINGTON, DC - MAY 21: FBI Director James Comey testifies during a Senate Judiciary Committee hearing on Capitol Hill, May 21, 2014 in Washington, DC. The committee is hearing testimony on oversight of the Federal Bureau Of Investigation. (Photo by Mark Wilson/Getty Images)
Now playing
02:45
James Comey, star witness
trump comey luck
PHOTO: CNN
trump comey luck
Now playing
00:35
Trump on Comey: I wish him luck
WASHINGTON, DC - MAY 03: Director of the Federal Bureau of Investigation, James Comey testifies in front of the Senate Judiciary Committee during an oversight hearing on the FBI on Capitol Hill May 3, 2017 in Washington, DC. Comey is expected to answer questions about Russian involvement into the 2016 presidential election. (Photo by Zach Gibson/Getty Images)
PHOTO: Zach Gibson/Getty Images
WASHINGTON, DC - MAY 03: Director of the Federal Bureau of Investigation, James Comey testifies in front of the Senate Judiciary Committee during an oversight hearing on the FBI on Capitol Hill May 3, 2017 in Washington, DC. Comey is expected to answer questions about Russian involvement into the 2016 presidential election. (Photo by Zach Gibson/Getty Images)
Now playing
01:07
Catch up on the Comey memo scandal
WASHINGTON - MAY 31:  The exterior view of the south side of the White House is seen May 31, 2005 in Washington, DC. Vanity Fair Magazine reported that former FBI official W. Mark Felt claimed himself was ?Deep Throat,? the anonymous source who provided information to Washington Post reporter Bob Woodward?s famous Watergate investigation report that led to the former President Richard Nixon's resignation.  (Photo by Alex Wong/Getty Images)
PHOTO: Alex Wong/Getty Images
WASHINGTON - MAY 31: The exterior view of the south side of the White House is seen May 31, 2005 in Washington, DC. Vanity Fair Magazine reported that former FBI official W. Mark Felt claimed himself was ?Deep Throat,? the anonymous source who provided information to Washington Post reporter Bob Woodward?s famous Watergate investigation report that led to the former President Richard Nixon's resignation. (Photo by Alex Wong/Getty Images)
Now playing
01:00
White House: Trump won't block Comey testimony
WASHINGTON, DC - JANUARY 22: U.S. President Donald Trump (L) shakes hands with James Comey, director of the Federal Bureau of Investigation (FBI), during an Inaugural Law Enforcement Officers and First Responders Reception in the Blue Room of the White House on January 22, 2017 in Washington, DC. Trump today mocked protesters who gathered for large demonstrations across the U.S. and the world on Saturday to signal discontent with his leadership, but later offered a more conciliatory tone, saying he recognized such marches as a "hallmark of our democracy." (Photo by Andrew Harrer-Pool/Getty Images)
PHOTO: Pool/Getty Images North America/Getty Images
WASHINGTON, DC - JANUARY 22: U.S. President Donald Trump (L) shakes hands with James Comey, director of the Federal Bureau of Investigation (FBI), during an Inaugural Law Enforcement Officers and First Responders Reception in the Blue Room of the White House on January 22, 2017 in Washington, DC. Trump today mocked protesters who gathered for large demonstrations across the U.S. and the world on Saturday to signal discontent with his leadership, but later offered a more conciliatory tone, saying he recognized such marches as a "hallmark of our democracy." (Photo by Andrew Harrer-Pool/Getty Images)
Now playing
02:09
Trump and Comey's ups and downs
NEW LONDON, CT - MAY 17: US President Donald Trump looks on as he hands out diplomas to Coast Guard cadets at the commencement ceremony at the U.S. Coast Guard Academy, May 17, 2017 in New London, Connecticut. This is President Trump's second commencement address since taking office and comes amid controversy after his firing of FBI Director James Comey. (Photo by Drew Angerer/Getty Images)
PHOTO: Drew Angerer/Getty Images
NEW LONDON, CT - MAY 17: US President Donald Trump looks on as he hands out diplomas to Coast Guard cadets at the commencement ceremony at the U.S. Coast Guard Academy, May 17, 2017 in New London, Connecticut. This is President Trump's second commencement address since taking office and comes amid controversy after his firing of FBI Director James Comey. (Photo by Drew Angerer/Getty Images)
Now playing
01:06
Gergen: Invoking executive privilege a mistake
WASHINGTON, DC - JUNE 23:  FBI Director James Comey participates in a news conference on child sex trafficking, at FBI headquarters, June 23, 2014 in Washington, DC. Director Comey said that 168 juveniles have been recovered in a nationwide operation targeting commercial child sex trafficking.  (Photo by Mark Wilson/Getty Images)
PHOTO: Mark Wilson/Getty Images
WASHINGTON, DC - JUNE 23: FBI Director James Comey participates in a news conference on child sex trafficking, at FBI headquarters, June 23, 2014 in Washington, DC. Director Comey said that 168 juveniles have been recovered in a nationwide operation targeting commercial child sex trafficking. (Photo by Mark Wilson/Getty Images)
Now playing
01:05
Who is James Comey?
sean spicer white house press briefing executive privilege sot _00000122.jpg
sean spicer white house press briefing executive privilege sot _00000122.jpg
Now playing
02:15
Spicer mum on WH invoking executive privilege
WASHINGTON, DC - JANUARY 22: U.S. President Donald Trump (C) shakes hands with James Comey, director of the Federal Bureau of Investigation (FBI), during an Inaugural Law Enforcement Officers and First Responders Reception in the Blue Room of the White House on January 22, 2017 in Washington, DC. Trump today mocked protesters who gathered for large demonstrations across the U.S. and the world on Saturday to signal discontent with his leadership, but later offered a more conciliatory tone, saying he recognized such marches as a "hallmark of our democracy." (Photo by Andrew Harrer-Pool/Getty Images)
PHOTO: Andrew Harrer/Pool/Getty Images/FILE
WASHINGTON, DC - JANUARY 22: U.S. President Donald Trump (C) shakes hands with James Comey, director of the Federal Bureau of Investigation (FBI), during an Inaugural Law Enforcement Officers and First Responders Reception in the Blue Room of the White House on January 22, 2017 in Washington, DC. Trump today mocked protesters who gathered for large demonstrations across the U.S. and the world on Saturday to signal discontent with his leadership, but later offered a more conciliatory tone, saying he recognized such marches as a "hallmark of our democracy." (Photo by Andrew Harrer-Pool/Getty Images)
Now playing
03:04
Source: Comey thinks Trump tried influencing him
PHOTO: Joe Raedle/MANDEL NGAN/AFP/Getty Images
Now playing
01:29
Will Trump keep Comey from testifying?
lindsey graham soft power baltics hearing bts_00010925.jpg
lindsey graham soft power baltics hearing bts_00010925.jpg
Now playing
02:53
Graham rips Comey for misleading Congress

Story highlights

Clapper said his statements aren't "exculpatory"

He warned about federal checks and balances eroding

(CNN) —  

Former Director of National Intelligence James Clapper said Sunday that he thinks US institutions are under assault from President Donald Trump.

“I think in many ways our institutions are under assault both externally – and that’s the big news here is the Russian interference in our election system – and I think as well our institutions are under assault internally,” Clapper told anchor Jake Tapper on CNN’s “State of the Union.”

Pressed if he meant US institutions were under assault internally from the President, Clapper responded, “Exactly.”

Clapper called on the other branches of the federal government to step up in their roles as a check on the executive.

“The founding fathers, in their genius, created a system of three co-equal branches of government and a built-in system of checks and balances,” Clapper said. “I feel as though that is under assault and is eroding.”

RELATED: The many paths from Trump to Russia

Democrats and several Republicans in Congress have publicly mulled pressing the Department of Justice to appoint a special prosecutor or establishing an independent investigative body that could look into allegations of potential collusion between Russia and the Trump campaign in what the US intelligence community says was Moscow’s efforts to influence the US election.

The Senate must confirm a new FBI director once Trump names a candidate; that FBI director will take a lead role in the Russia investigation.

Utah Republican Sen. Mike Lee advocated on “Fox News Sunday” that Trump appoint Judge Merrick Garland to head the FBI. Josh Holmes, a former aide to Senate Majority Leader Mitch McConnell, said later on the program that the Republican leader had just called him to say he would support Garland for FBI’s top spot.

Garland was President Barack Obama’s pick to replace Supreme Court Justice Antonin Scalia after Scalia’s death last year. If appointed and confirmed as FBI director, Garland’s appointment would create a vacancy on the US Circuit Court of Appeals for the District of Columbia, which has jurisdiction over the DC area and federal agencies, making it one of the highest legal authorities in the country short of the Supreme Court.

Can’t refute or confirm collusion questions

Clapper also said Sunday that the President and the White House are wrong to cite Clapper’s previous Senate testimony on the questions about alleged collusion between the Trump campaign and Russia as proof that no such collusion exists, emphasizing that no one should portray his comments as “exculpatory” – something Trump has done repeatedly on Twitter.

“The bottom line is I don’t know if there was collusion, political collusion,” Clapper told Tapper. “I don’t know of any evidence to it. So I can’t refute it, and I can’t confirm it.”

Clapper told NBC in March that he didn’t know of any evidence that demonstrated collusion between Russia and the Trump campaign. At a Senate Judiciary subcommittee hearing earlier this month, Clapper clarified that statement, saying he was also unaware of the FBI’s investigation into the matter until Comey made it public in March.

At that subcommittee hearing, former acting Attorney General Sally Yates, whom Trump fired in January for refusing to defend his initial temporary ban on visitors from several Muslim-majority countries and suspension of the entry of Syrian refugees, declined to answer the question of whether there was evidence of collusion publicly; in her answer, she also noted that Clapper had been unaware of the FBI investigation.

Clapper said Sunday that his “standard practice” as the leader of the intelligence community during the Obama administration was to defer to the FBI on any counterintelligence investigations.

He noted the intelligence community’s joint assessment declaring Russia had interfered in the 2016 election did not contain any reporting about political collusion.

“I did not have any evidence,” Clapper said, again noting he was unaware of the executive branch investigation into allegations of collusion.

Comey and Trump

On Friday, Trump raised eyebrows by tweeting a warning to Comey, whom he fired unexpectedly on Tuesday, about leaking information to the media, saying he “better hope that there are no ‘tapes’ of our conversations before he starts leaking to the press.”

In his news briefing later that day, White House press secretary Sean Spicer declined repeatedly to explain what the tweet meant or address questions about whether there were recording devices in the Oval Office.

Trump and Comey had a private dinner in the White House on January 27 in which a source close to Comey said the President asked the FBI director to pledge his loyalty, which Comey, who reportedly was taken aback by the request, refused to do.

The dinner was on the same day that Yates went to the White House to warn the administration about since-ousted national security adviser Michael Flynn’s potential vulnerability to Russian blackmail and that Trump issued the executive order restricting travel from several majority-Muslim nations.

Clapper said Sunday that he spoke with Comey prior to the dinner while at an event at FBI headquarters in Washington.

“He mentioned to me the invitation he had from the President for dinner,” Clapper said. “He was – my characterization – uneasy with it both from the standpoint of the optic of compromising his independence and the independence of the FBI.”