"The big story is Russian interference in our process," he told CNN's Anderson Cooper on "AC360." "And they exceeded their wildest dreams and expectations, I'm sure, by the discord, doubt and disruptions they have caused in our political process."
Clapper told Cooper he thinks the Russians are "emboldened now to be even more aggressive." He said Watergate "pales" in comparison to the probe into Russian meddling in the 2016 election.
"They're not going to stop," he said.
Clapper also made a striking statement about President Donald Trump's posture throughout his campaign and while in office.
"I think the President himself has undertaken -- whether intentionally or not -- assaults on our institutions," he said, pointing to times Trump spoke negatively about members of the intelligence community and individual judges as examples.
When Cooper asked Clapper whether he feels the President is a "threat to democracy," Clapper said he believes Trump is a threat to "our system."
However, when he testified before a Senate judiciary subcommittee, he said he was not aware of any evidence
demonstrating collusion between Trump's campaign and Russia. He said he had been unaware of an FBI investigation into the matter until Comey announced it publicly at a House hearing in March.
On Thursday, Clapper commended Comey's testimony. During the three-hour hearing, Comey answered questions about the FBI's Russia investigation, his private interactions with Trump and how he handled the Hillary Clinton email probe.
When Cooper asked if it comes down to a "he said, he said" about the substance of Comey and Trump's conversations, whom would he trust, Clapper answered that he trusts Comey over Trump.
"There's absolutely no doubt in my mind that I have and always will trust the word and the integrity of Jim Comey," Clapper said.