In September, 1972, about ten weeks after the Watergate break-in, Carl Bernstein and Bob Woodward huddled in the vending-machine room at the Washington Post’s old headquarters, on Fifteenth Street. Most days, the two reporters met there before presenting their latest scoops to the top editors. This was a particularly nerve-racking meeting. They had confirmed that John Mitchell, Richard Nixon’s former Attorney General and the manager of his reëlection campaign, had controlled a secret fund that paid for the break-in.

Bernstein told me that he felt a chill, unlike anything he has felt since. He put a dime in a machine for some coffee and turned to Woodward. “Oh, my God,” he said, “the President is going to be impeached.”

Woodward agreed, and they decided that they would never use the “I-word,” as they called it, because they didn’t want anyone to think they had a political agenda. “It wasn’t our job how the information was acted upon,” Bernstein said. They left the coffee-room anecdote out of “All the President’s Men,” which was published in June, 1974, in the middle of the House impeachment hearings.

That July, the Supreme Court forced Nixon to release the “smoking gun” tape, which revealed that Nixon had instructed H. R. Haldeman, his chief of staff, to tell the C.I.A. to block the F.B.I. probe of Watergate. This was clear obstruction of justice, and it triggered key Republicans on Capitol Hill to break with Nixon. In August, all but certain to be impeached and removed from office, he resigned.

After a week of revelations about Donald Trump’s efforts to impede the F.B.I. investigation into his campaign, I asked Bernstein if he thought we had reached the turning point of 1972, or that of 1974.

“We’ve reached the threshold in which discussion of obstruction of justice is reasonable,” he said.

The current time line of Trump’s actions in response to the investigation is damning. On January 26th, Sally Yates, the acting Attorney General, informed the White House that Michael Flynn, Trump’s national-security adviser, had lied to officials about his conversations with Sergey Kislyak, the Russian Ambassador. The next day, Trump asked the F.B.I. director, James Comey, to pledge his loyalty to him, which Comey declined to do.

On February 13th, Flynn resigned, after the Washington Post reported that he had lied to Vice-President Mike Pence and others. On February 14th, Trump asked Comey to back off his investigation of Flynn. “I hope you can see your way clear to letting this go, to letting Flynn go” Trump told Comey, according to the Times.

On March 20th, Comey testified before the House Intelligence Committee that the F.B.I. was indeed investigating “the nature of any links between individuals associated with the Trump campaign and the Russian government, and whether there was any coördination between the campaign and Russia’s efforts.” Afterward, the President asked Mike Rogers, the director of the National Security Agency, and Dan Coats, the director of national intelligence, to make public statements that there was no evidence of such coördination, and asked intelligence officials if they could help shut down the investigation, according to the Washington Post. On Tuesday, in testimony before the Senate Armed Services Committee, Coats refused to confirm or deny this account. “On this topic as well as other topics, I don’t feel it’s appropriate to characterize discussions and conversations with the President,” he said.

In early May, according to the Times, “Comey asked the Justice Department for more prosecutors and other personnel to accelerate the bureau’s investigation.” On May 9th, Trump fired Comey, and claimed that he was doing so at the recommendation of Rod Rosenstein, the Deputy Attorney General. The next day, in an interview with NBC News’s Lester Holt, Trump admitted that he had fired Comey because he was unhappy with the Russia probe, which he said was “a made-up story.”

On the same day, Trump hosted Kislyak and Sergey Lavrov, the Russian foreign minister, at the White House, at Vladimir Putin’s request. At the meeting, Trump reportedly told Lavrov and Kislyak that Comey was “a real nut job,” adding, “I faced great pressure because of Russia. That’s taken off.”

There is now significant evidence that Trump has been trying to cover up something related to the F.B.I. investigation_._ We just don’t know what it is. In Watergate, Bernstein noted, “we knew there was a break-in and also that there was a massive campaign of political espionage and sabotage to undermine the political opposition.” But with Trump, he went on, it could be a range of offenses: “Is it specific acts of collusion? Is it his financial dealings with ethno-Russians and countries of the former Soviet empire or those of others around him? Is it about obstructing these investigations because they’ll reveal inappropriate contacts between the campaign and people acting in the interests of a hostile foreign power, perhaps including the President? We don’t know yet.”

Certainly, the parade of senior intelligence and Justice Department officials who have commented publicly on the case—Yates, Comey, Rogers, and James Clapper, the former director of national intelligence—believe that the Trump campaign’s Russia ties merit serious investigation. On Tuesday, John Brennan, the former C.I.A. director, testified, in a House Intelligence Committee hearing, that he saw “intelligence that revealed contacts and interactions between Russian officials and U.S. persons involved in the Trump campaign.” He was concerned enough that he passed along information to the F.B.I., so that it could investigate.

When asked by Trey Gowdy, the Republican congressman from South Carolina, whether he saw “evidence of collusion, coördination, conspiracy between Donald Trump and Russian state actors,” Brennan did not rule it out. “I saw information and intelligence that was worthy of investigation by the Bureau to determine whether or not such coöperation or collusion was taking place,” he said. The takeaway for some Republicans is that there’s no evidence of collusion. But it should be that we need thorough, unimpeded investigations by the F.B.I., Congress, and the press—the ones that Trump has tried to thwart at every turn—to answer Gowdy’s question.

In April, after Trump declined to speak at the White House Correspondents’ Association’s annual dinner in Washington, Bernstein and Woodward accepted an invitation to address the crowd of journalists. Bernstein paid homage to his old partner by reading a list of lessons he had learned from Woodward. On Tuesday, he told me that that the first lesson was particularly important to Trump reporting.

“Almost inevitably, unreasonable government secrecy is the enemy—and, usually, the giveaway about what the real story might be,” Bernstein said. "And when lying is combined with secrecy there is usually a pretty good roadmap in front of you.” He added, “Yes, follow the money. But also follow the lies.”