The White House declined on Friday to say whether President Donald Trump is recording conversations in the Oval Office or those with dinner guests in the White House.
Trump escalated his feud on Friday morning with fired FBI chief James Comey, tweeting an implication there are secret recordings of one of their private conversations from earlier this year.
Trump, writing on the Twitter social media platform, said, "James Comey better hope that there are no 'tapes' of our conversations before he starts leaking to the press!"
Asked by a reporter at the daily briefing about that tweet, White House press secretary Sean Spicer repeatedly said, "The president has nothing further to add on that."
Spicer said, however, that the message was "not a threat. He simply stated a fact. The tweet speaks for itself."
WATCH: Trump Tweet ‘Not A Threat,’ Spicer Says
Historians say presidents are believed to have stopped routinely recording visitors without their knowledge when the Oval Office recording system used by President Richard Nixon was exposed in 1973. A subsequent subpoena of the tapes helped to spark the unraveling of support for Nixon before he resigned a month into the impeachment proceedings over Watergate.
"I don't actually think Trump is recording his conversations. It would be a phenomenally shortsighted move, as recordings could be subpoenaed or otherwise leak out," Nicole Hemmer, assistant professor of presidential studies at the University of Virginia's Miller Center, told VOA. "The trend in the White House has been toward fewer paper trails, not more. As far as we know, recordings stopped with Nixon, and even private diaries stopped with [Ronald] Reagan after his were subpoenaed during the Iran-Contra affair."
Question of credibility
White House spokesman Spicer on Friday also answered "no" to a question about whether Trump, at a January 27 White House dinner, had asked Comey to pledge loyalty to the president.
The second-ranking Senate Democrat on Friday called Trump "dangerous because he may be obstructing justice" in the investigation of Russia's involvement in the 2016 presidential election and possible ties to the Trump campaign.
The president's "credibility has been destroyed," added Senator Dick Durbin of Illinois, who sits on the Senate Judiciary Committee.
The ranking member of the House subcommittee on government operations, Gerry Connolly, questioned whether the president was "unhinged" for issuing the tweet, saying that in addition to obstruction of an investigation, the president now was engaging in "witness intimidation."
Trump on Tuesday fired Comey, who was leading an investigation into the alleged ties between the president's campaign and Russia.
Request for recordings
Ranking members on the House Judiciary Committee and Oversight and Government Reform Committee sent a letter Friday to the White House, saying "it is a crime to intimidate or threaten any potential witness with the intent to influence, delay or prevent their official testimony."
Congressmen John Conyers Jr. and Elijah Cummings addressed it to White House Counsel Don McGahn, asking whether the recordings actually existed, and saying that if they did, "we request copies of all recordings in possession of the White House regarding this matter."
They went on to say, "We believe Congress should immediately seek the testimony of Director Comey to better understand the circumstances surrounding these events ... ."
In comments Friday to MSNBC, former Director of National Intelligence James Clapper said he did not know whether there was any collusion between Trump campaign officials and Russia. Nor should he know, he said, because the issue is the FBI's responsibility.
Clapper said his practice was always to defer to the FBI director "on whether, when and what to tell me about a counterintelligence investigation."
His comment contradicted a Trump tweet saying Clapper did not believe there was collusion.
White House officials insist Comey's firing had nothing to do with the Russia probe, though the president appeared to have undermined that assertion during a televised interview Thursday.
The president is also facing criticism after acknowledging in the NBC interview on Thursday that he repeatedly asked Comey whether he was under investigation.
Legal analyst Bradley Moss, who specializes in national security issues, called such an exchange "highly inappropriate" at a minimum.
"There is supposed to be a line that is not crossed, including asking the FBI if you yourself are the target of the investigation," Moss told VOA.
But Moss, deputy executive director of the James Madison Project, a Washington-based organization that promotes government accountability, added it is "difficult to say if it is actually illegal, since Comey allegedly responded that Trump was not under investigation."
Laurence Tribe, a Harvard professor specializing in constitutional law, wrote on Twitter that it is "now totally clear that Trump's firing of Comey was an obstruction of justice. That was the first article of impeachment against Nixon."
Nixon resigned in 1974 less than a month after the House of Representatives began impeachment proceedings against him.