Here's a barometer for how troubled the Trump presidency is: John Dean is back in the spotlight. Dean was Richard Nixon's White House counsel and a central character during the Watergate years. He was awaiting a television appearance when I ran into him last month in the green room of CNN’s Los Angeles bureau.

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).

Does that not sound like a parallel to you?

Does that not sound like a parallel to you?" Dean asked with a laugh. Beyond that, by Comey's telling, Trump made the request directly to the FBI director, Dean noted. "There was no intermediary.

Dean, who is now 78, peered over his glasses, reading court documents that explored the varying definitions of obstruction of justice in different judicial circuits. The legal questions he was weighing about Trump’s conduct were the same ones that White House officials grappled with during those fraught months before Nixon decided to resign, he said.

What would constitute an obstruction of justice charge during an impeachment proceeding versus a legal proceeding? Was the FBI's investigation of Flynn an "active judicial proceeding" at the time of the Trump-Comey conversation in the Oval Office? If Trump did indeed utter those loaded words about Flynn to Comey, would anyone be able to discern his motive or intent?

The month that shook Washington

House Republicans pass legislation to repeal and replace Obamacare, celebrating with Trump at the White House.

Trump fires FBI Director James Comey, initially attributing the dismissal to his handling of the 2016 investigation into Hillary Clinton's emails.

Trump says Comey was fired because "he wasn't doing a good job."

White House deputy press secretary Sarah Huckabee Sanders says Trump had been thinking about firing Comey since Election Day.

Trump tells NBC News he was thinking of "this Russia thing" when he decided to fire Comey.

Trump tweets " is not possible for my surrogates to stand at podium with perfect accuracy!"

Trump tweets that Comey "...better hope that there are no 'tapes' of our conversations before he starts leaking to the press!"

Citing current and former US officials, The Washington Post reports Trump told Russian Foreign Minister Sergey Lavrov and Russian ambassador to the US Sergey Kislyak about highly classified intelligence from an ally. Israel was later revealed as the source of some of the information.

National Security Adviser H.R. McMaster tells reporters the Post story "as reported is false."

Trump tweets he has "absolute right" to share information with Russia.

The New York Times reports on a memo from Comey detailing a request from Trump to end the investigation into former national security adviser Michael Flynn.

"We should take our oversight responsibilities seriously regardless of who is in power," House Speaker Paul Ryan tells reporters.

Trump tells graduates at the US Coast Guard Academy that "no politician in history, and I say this with great surety, has been treated worse or more unfairly."

Department of Justice appoints former FBI Director Robert Mueller as special counsel to oversee the federal investigation into Russian interference in the 2016 election.

Trump has set the stage for lengthy investigation into those matters. He was unequivocal when asked whether he had attempted to impede the investigation into Flynn's ties to Russia. "No. No," he told a reporter during a recent press conference in the East Room of the White House. "Next question."

Comey is expected to contradict Trump's account when he testifies publicly before the Senate Intelligence Committee June 8. And in another blockbuster development last week, The Washington Post reported that Trump called Adm. Michael S. Rogers, the director of National Security Agency, and Dan Coats, the Director of National Intelligence, asking them to publicly deny any evidence of collusion between his campaign and the Russian government during the the 2016 election. The President's request, multiple current and former US officials told CNN, came shortly after Comey's March 20 testimony before the House Intelligence Committee confirming the existence of the investigation.

The probe is expected to go underground now that Robert Mueller, the special counsel named to investigate allegations of collusion between Russian officials and Trump campaign aides, is taking the helm. (In another Nixon-era throwback, Mueller is bringing James Quarles, an assistant special prosecutor during Watergate, with him.)

But the cloud of Russia over the Trump administration is unlikely to dissipate. Even before the probe grew to "Watergate size and scale," as Sen. John McCain recently put it, it has been impossible for Trump to avoid comparisons to Nixon.

Like Nixon, Trump has proven himself to be erratic, insecure and image-obsessed

The lines have been drawn for years. In the 1980s, Nixon once wrote Trump to praise his appearance on Phil Donahue's talk show and said his wife predicted that "whenever you decide to run for office you will be a winner!" Like Nixon, Trump has proven himself to be erratic, insecure and image-obsessed. As his presidency has progressed, he has grown increasingly angry at the news media, who he calls the enemy, and the Russia probe, which he called a "witch hunt."

Four decades ago, Nixon used much of the same terminology, calling the Watergate investigation a "witch hunt." "Never forget," he told his then-national security adviser Henry Kissinger in a taped conversation a year earlier, "The press is the enemy. The establishment is the enemy. The professors are the enemy… Write that on a blackboard 100 times and never forget it."

Kissinger oddly resurfaced in the news after meeting with Trump the morning following Comey’s firing. The White House said the meeting had been previously scheduled.

Even Trump's sense of injustice is strikingly similar to the Nixon days. Four months after taking office, Trump remains obsessed with the 2016 election results and describes the Russia investigation as "a pure excuse for the Democrats having lost an election that they should have easily won."

He recently complained to the graduating class of the United States Coast Guard Academy that, "no politician in history, and I say this with great surety, has been treated worse or more unfairly."

"You can't let them get you down," Trump said with echoes of the aggrieved tone that Nixon once adopted. "You can't let the critics and the naysayers get in the way of your dreams.

To Nixon historian John A. Farrell, most of the historical parallels between Trump's conduct and Watergate seemed coincidental until Trump fired Comey. That struck Farrell as "virtually identical" to Nixon’s "Saturday Night Massacre," in which the President fired the special prosecutor investigating Watergate.

The similarities got even more eerie with the added revelations that Trump appeared to apply pressure on Comey to ease up on the Flynn investigation in their disputed conversation. A timeline began to emerge suggesting motive, said Farrell, the author of "Richard Nixon: The Life," which was published earlier this year.

There are going to be lots of differences, but the elemental act is very similar

"In both cases, you have an American president accused, or suspected, of participating in the undermining of an election, facing off against one of the nation's top law enforcement officials, and when that official didn't back off -- firing them," Farrell said. "There are going to be lots of differences, but the elemental act is very similar.

Still, Farrell noted that we now have the advantage of understanding Nixon's motives. We don't yet know what was going through Trump's mind during his conversations with Comey.

It could be that this was a humanitarian gesture on the part of the President to help out his friend, Mike Flynn, and not a veiled suggestion that Comey back off," Farrell said. "Of course, now we've got a special counsel named to investigate all this, and try to find out whether it was Trump being Trump, or whether it was Trump being Nixon.

A handful of Democrats have already called for Trump's impeachment, but it is far too early to tell whether the President is really facing his own Watergate.

We don't know if there are any tapes -- a possibility that Trump raised in a curious May 12 tweet threatening Comey. Republicans are firmly in control of the House -- where any impeachment proceeding would originate -- and GOP lawmakers are standing with the President for now, though some have expressed alarm about his conduct.

CNN presidential historian Tim Naftali, the founding director of the Richard Nixon Presidential Library and Museum, noted that the investigation into Trump's motives and his actions is only just beginning.

The question is the same. Did the President, intentionally, try to deflect or otherwise weaken an FBI investigation?

"The question is the same," Naftali said. "Did the President, intentionally, try to deflect or otherwise weaken an FBI investigation? In Nixon's case, he did, repeatedly, in different ways -- whether it was agreeing to use the CIA to distract the FBI, or by indirectly coaching some of his staff about what to say to the FBI under oath. So it's not a surprise that people would say this reminds us of the issues surrounding Nixon before the tapes came out.

These were the kinds of questions people were asking -- did President Nixon interfere, in any way, in any investigation? And it was an open question until the tapes sealed the issue," Naftali said. "In the case of Donald Trump, it's an open question.

A question that may not be answered until well into his presidency.