Appearing on CNN's State of the Union, former Director of National Intelligence James Clapper defended former FBI Director James Comey and accused President Donald Trump of undermining the U.S. government's system of checks and balances.

Speaking with host Jake Tapper, Clapper stated that the U.S. is currently under assault from "external and internal forces" -- admitting that he was referring to the president when he spoke of internal threats.

Addressing the stunning firing of FBI Director James Comey, host Tapper asked Clapper if Trump had finally "crossed a line."

"Let's take a wider view of this for one second and then get back to more detailed questions," Tapper began. "This week with the president firing the FBI director while this investigation is going on, and then saying that he was thinking about the Russia probe when he was making the decision, have we crossed a line here?"

"Well, I will just say that the developments of the past week are very bothersome, very disturbing to me," Clapper replied. "I think in many ways, our institutions are under assault externally and that's the big news here, the Russian interference in our election system. And I think as well our institutions are under assault internally."

"Internally from the president?" Tapper pressed.

"Exactly," Clapper quickly replied.

"Because he's firing the checks and balances?" Tapper asked.

"Well I think you know, the founding fathers put in place a system of three co-equal branches of government, and a built-in system of checks and balances, and I feel as though that's under assault and is eroding," Clapper explained.

"Are you surprised at how quiet Republicans on Capitol Hill have been?" Tapper asked.

"I can't say I think each senator or congressman has got to say something," Clapper explained. "I hope they will think in terms of their own conscience. I can't characterize it as being surprised, I just hope they will speak up."

Watch the video below via CNN: