The White House on Friday declined to deny that President Donald Trump is recording conversations he is having in the Oval Office.

Press Secretary Sean Spicer began his back-and-forth with reporters Friday by saying Trump told him he has “nothing to add” to a morning tweet in which he suggested he has “tapes” of private conversations with James Comey, the former FBI director whom he fired on Tuesday. The president threatened to release them should Comey talk to the media.

Trump’s top spokesman, back at the briefing room podium after two days on Naval Reserve duty, was  also asked if anyone in the White House has a recording of a Trump-Comey dinner early in Trump’s presidency that the president referenced during a Thursday interview with NBC News. Spicer replied: “I’m not aware of that.”

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Pressed about whether Trump is recording conversations in the Oval Office, Spicer would only say that Trump told him he has no further comment about the remarkable tweet.

The questions were prompted by a morning tweet series from Trump that included one of his most brazen since being sworn in on Jan. 20: “James Comey better hope that there are no ‘tapes’ of our conversations before he starts leaking to the press!”

James Comey better hope that there are no “tapes” of our conversations before he starts leaking to the press!

— Donald J. Trump (@realDonaldTrump) May 12, 2017

Spicer’s non-denials about recordings of Trump conversations provided a poignant end to a week that conjured memories of former President Richard Nixon.

By suggesting he has tapes of Comey, who until Tuesday evening was overseeing the bureau’s investigation of Russian meddling in the 2016 presidential election and possible collusion between Moscow and Trump’s campaign, the president immediately intensified comparisons to Nixon’s Watergate scandal. The 37th president’s secret recordings of his conversations were part of the web of problems surrounding the scandal that ultimately led to his resignation.

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Kevin Mattson, a history professor at Ohio University, this week said “there always has been this natural comparison between Trump and Nixon.”

Comey’s firing led to comparisons to the 1973 “Saturday Night Massacre,” which led to the resignations of Attorney General Elliot Richardson and Deputy Attorney General William Ruckelshaus, who refused to fire Watergate Special Prosecutor Archibald Cox. Solicitor General Robert Bork eventually fired Cox. 

“The Watergate crime was one tied to an election, which we also see here,” Mattson said, adding it is too soon to tell how Comey’s firing and the fallout will affect Trump’s presidency.

“But the ‘Saturday Night Massacre’ was definitely a turning point for Nixon. Everything turned downward for Nixon after that,” he said. “By that time in Nixon’s presidency, his credibility across the board was so low that people thought his fate should be up to the House and Senate. With Trump, his credibility with his base is still very high.”

For their part, Democrats are demanding Trump either confirm there are no tapes or hand them over. In a letter to White House Counsel Donald McGahn, House Judiciary ranking member John Conyers Jr. and Oversight and Government Reform ranking member Elijah E. Cummings requested “all documents, memoranda, analyses, emails, and other communications relating to the President’s decision to dismiss Director Comey—a decision which the President declared yesterday he planned to make “regardless of [the Deputy Attorney General’s] recommendation”—and all discussions with Director Comey.” 

Rema Rahman contributed to this story