Former White House aide John Dean on Wednesday compared his testimony against President Richard Nixon to the testimony of European Union Ambassador Gordon Sondland.

"This has been called by some commentators a John Dean moment," CNN host Jake Tapper noted during a break in the testimony. "And there is no person I can think of who is better qualified to weigh in on that than John Dean."

"Is he the John Dean of this impeachment inquiry?" Tapper wondered.

"His statement certainly caught the Republicans off guard," Dean replied. "They didn't pick away -- just a few little picky points."

European Union ambassador Gordon Sondland's testimony before the House of Representatives' impeachment inquiry on Wednesday generated several startling revelations, including confirmation of an explicit quid-pro-quo deal involving investigations into former Vice President Joe Biden.

CNN's Jake Tapper described Sondland's testimony as " a monumental and historic moment on what may turn out to be the worst day with the most damning evidence for President Trump in the impeachment inquiry."

He then laid out all the ways that Sondland has been very bad news for the president.

"Sondland directly implicated the president in directing the operation to pressure Ukraine," Tapper explained. "Sondland is testifying that there very clearly was a quid pro quo -- this was for a White House visit for the Ukrainians in exchange for an announcement about an investigation into the company Burisma and the Bidens. Now, Sondland later said it became clear to him that the quid pro quo also, he presumed, was tied to the holdup of hundreds of millions of dollars in military aid that Ukraine desperately needed."