Former Director of National Intelligence James Clapper on Sunday said the democratic institutions of the United States are under attack as evidenced by President Trump's termination of former FBI Director James Comey.

"I think in many ways our institutions are under assault," Clapper, who worked in the Obama administration, told "State of the Union" host Jake Tapper on CNN. "Both externally, and that's the big news here, is Russian interference in our election system. And I think as well our institutions are under assault internally."

Comey's termination was "another victory" for Russia, Clapper added during a separate appearance on ABC.

Democrats have expressed concerns about the Trump administration firing Comey, whose agency is investigating possible collusion between Russia and the Trump campaign.