Earlier that evening, The New York Times published an explosive story that said President Donald Trump asked then-FBI Director James Comey to back off the investigation of his former national security advisor, Michael Flynn. It was the latest -- and perhaps strongest -- sign that Trump was exposing himself to a potential obstruction of justice charge.

Dean, who famously told Nixon that the cover-up was "a cancer on the presidency," marveled at how -- almost 43 years after the House Judiciary Committee voted to impeach Nixon for obstruction of justice -- there's sudden debate over whether lawmakers should charge Trump with the same crime.

That won't happen anytime soon and Trump has categorically denied that he attempted to impede Comey's investigation. But Dean noted that Nixon also strenuously denied any knowledge of a cover-up "until I told him on March 21st of 1973."

The tapes Nixon kept of his conversations proved that was a falsehood. "They showed that the first week after the arrest at the Watergate, on June 23 (1972), Nixon authorized a plan where his chief of staff, Bob Haldeman, was to call in the CIA, who was to go over and tell the FBI to stop the investigation of Watergate," Dean told me. (That June 23 recording became the "smoking gun" tape).