Just when you thought it was safe to go back in the water. Donald Trump is running for president again. That was not a prospect Bob Woodward had to deal with when Richard Nixon resigned in 1974, after Woodward and his Washington Post colleague Carl Bernstein cracked open the Watergate scandal.

“Our long national nightmare is over,” declared Nixon’s successor, Gerald Ford, and it was. Nixon faded into jowly retirement. But Trump yearns to regain the crown.

Woodward spoke to the Guardian by phone six hours before the disgraced one-term, twice-impeached president took the stage at Mar-a-Lago, his gaudy personal Xanadu in Florida, to announce what might or might not be the greatest political comeback of all time.

Does Woodward, who at 79 has written about nine American presidents, think Trump can win again? Or is Ron DeSantis, governor of Florida, hammer of wokeness, now the man to beat?

“Who knows? Trump’s got tens of millions of supporters. DeSantis is the flavour of the month. DeSantis may be the one. Maybe not. I remember in 1990, before the ’92 presidential election, with a bunch of friends making a list of the 50 people who might be the next president. [Bill] Clinton was not on the list [though] he would have put himself there. So who knows? You can’t record the future.”

But you can revisit the past. Trump pulled off an unlikely victory in 2016 in what many saw as an indictment of the media. While there was some fine reporting that left America in no doubt about what it was getting, there was also wall-to-wall cable news coverage and a constant pressure for his opponent, Hillary Clinton, to respond to Trump’s latest unhinged tweet. Are there lessons to learn?

Woodward says: “If you look back on 2016, there was a lot of good coverage but it was never enough. He was able to sell himself as a successful, wealthy businessman. What do we know about him now that we didn’t know in 2016? There is a lot of evidence, good reporting, investigations by some committees on the Hill, that actually he was not a successful businessman, he’s not wealthy. What’s the lesson from all that? Dig deeper and then, when you dig deep, dig deeper more and more and more.”

His image burnished by the reality TV show The Apprentice, the Trump of 2016 was able to essay the role of political outsider and swamp drainer. Now the novelty has worn off, he faces federal, state and congressional investigations and his four years in the Oval Office are a matter of record.

Woodward has contributed a trilogy of books – Fear, Rage and Peril (the last written with Robert Costa) – and now an audiobook, The Trump Tapes, presenting his 20 interviews with the president. The Guardian’s Lloyd Green called it “a passport to the heart of darkness”.

Woodward continues: “Now he’s going to run again and we in our business need to focus on what he did as president. That’s the office he’s running for. Yes, it’s a political office, and you see all the stories now about the politics of Trump running, people abandoning him, people sticking with him and so forth – that’s an important story.

“But the real scorecard is what he did as president and on foreign affairs, dealing with Kim Jong-un or [Vladimir] Putin or all this stuff that’s on the tapes. He made it personal. He ran it on instinct.”

Woodward describes the tapes as a “laboratory” for understanding Trump’s presidency. “My conclusions are very severe. He failed as president, failed to do his constitutional, moral, practical duty, and I think, not all, but most of the reporting should be on his presidency.”

Woodward cites the example of Trump’s tax cuts in 2017, estimated to cost $1.9tn over a decade, criticised as a handout to the rich and corporations at the expense of working families.

“I fault myself on this. I’ve not seen – maybe I’m not aware – of some really good reporting on the tax cut, how it happened exactly, who benefited. I wrote in one of my Trump books, Fear, that Gary Cohn engineered and drove it. The former president of Goldman Sachs benefited from that and you can surmise but I’d like to see my own paper or the Guardian or anywhere say: this is really who benefited from this.”

Nineteen of the Woodward/Trump interviews happened in person or by phone between autumn 2019 and August 2020, amid research for Rage.

This period included the police murder of George Floyd in Minneapolis and ensuing Black Lives Matter protests. Woodward suggested to Trump that both men had benefited from white privilege. The president was having none of it. He sneered: “You really drank the Kool-Aid, didn’t you? Just listen to you. Wow.”

This chapter of Trump’s tenure was also defined by the coronavirus, which emerged in China in late 2019 but which he downplayed, claiming it would vanish over the summer. Now, more than a million Americans have died of Covid-19.

In The Trump Tapes, Woodward interviews Robert O’Brien, the national security adviser who warned Trump the virus would be “the biggest national security threat you face in your presidency”, and his deputy, Matthew Pottinger, who likened it to the 1918 influenza pandemic that killed 650,000.

Woodward adds: “I discovered they issued this warning 28 January. I was as shocked as I’ve ever been as a reporter.”

By April, Woodward could not resist pushing Trump to meet the moment, telling him experts were saying he needed to mobilise the country, coordinate with intelligence agencies and work with foreign governments. Woodward argued: “If you come out and say, ‘This is a full mobilisation, this is a Manhattan Project, we are going – pardon the expression – balls to the wall’, that’s what people want.”

Had he crossed a line? His wife, Elsa Walsh, also a journalist, thought so. He recalls: “I did these interviews on speakerphone so I could record them with Trump’s permission. She was there many times and Trump knew that and then afterwards she said I was yelling at Trump and that I shouldn’t be doing that. I’m just supposed to ask questions. She berated me for this. It’s on the tape.”

But he insists: “It wasn’t an advocacy position. Trump had these coronavirus meetings and had virus deniers there and so the whole atmosphere was one of ‘Let’s not listen to the experts’. I knew some of these people and found out what they said and they were very specific and it had a logic to it, namely that overall Trump needed a world war two-style mobilisation to deal with this.

“I couldn’t talk to him so I passed it on and made it clear this is not me but this is my reporting from what the experts are saying. As I said to my wife, we’re in a different world. It’s the reporter who’s on the street and sees somebody shot. Go help them as a human being and then you phone in the story. This is of the magnitude that 1.1 million people died in this country because of the virus.”

By the summer, the scale of Trump’s failure and the price in death and grief were clear. In the tapes, Woodward asks: “Was there a moment in all of this last two months where you said to yourself, ‘Ah, this is the leadership test of a lifetime?’”

Trump replies, with dead finality: “No.”

Woodward reflects: “Even then, let alone now, it was the leadership test of a lifetime and just, ‘No’. It’s tragic. Not only did he conceal what he knew and deny it but it’s a crime. It’s a moral crime to know all this and not tell the people. I once asked him the job of the president and he said, ‘To protect the people.’ I’ve never heard about or read anywhere in my own reporting or in history where a president was so negligent.”

The last long interview took place on 21 July 2020. Woodward said things were bad. Trump did not understand so Woodward had to point out that 140,000 people had died. The president claimed to have Covid under control. Woodward asked, “What’s the plan?” Trump said there would be one in 104 days. Woodward wondered what he was talking about. Then he realised: the presidential election was 104 days away.

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Such exchanges are damning and ensure that in more than eight hours of conversations, by his own words shall Trump be condemned. Why, then, did he agree to talk? As the comedian Jimmy Kimmel put it: “Why are you agreeing to do 20 interviews on tape with the guy who took down Richard Nixon with tapes? With tapes!”

One answer is ego. Trump can be heard flattering “a great historian” and “the great Bob Woodward”. Woodward suggests: “I had been sceptical of the Steele dossier and the Russian investigation and had said so publicly. [Senator] Lindsey Graham, [Trump’s] supporter from South Carolina, had told him I would not put words in his mouth, which was true, and so he agreed to do these interviews.”

On the other side of the coin, this is a rare opportunity to hear the Woodward method. The Washington Post, where he has worked for half a century, observed that The Trump Tapes “offers a surprising window into the legendary investigative reporter’s process – a perennial focus of both mystique and critique”.

At times, Woodward indulges Trump’s streams of consciousness, airing of grievances and pathological narcissism. At others he cajoles, challenges or confronts. Woodward says: “He’ll talk and talk and talk but I ask questions, very specific questions. What are you doing about the virus? Tell me about Putin.”

He did miss one opening. He asked if, in the event of a close election in November, Trump would refuse to leave the White House. The president declined to comment.

“It was the only question he didn’t answer in eight hours – 600 questions – and I should have followed up. I should have said, ‘Wait a minute, why isn’t he answering that?’ I didn’t.”

Re-listening to all 20 interviews, and finding it such a different experience from reading the transcripts or listening to snatches on TV or the internet, convinced Woodward to release the recordings – a first in his long career. Raw and unfiltered, this is one instance where Trump does not benefit from a reporter “tidying up” his quotations to make him sound more lucid and less repetitive than he actually is.

“To be frank, it’s very surprising and it’s a learning experience at age 79, having done this so many years, that there’s something about hearing the voice that gives it an authenticity and power,” Woodward says. “Especially Trump. He doesn’t ever hem and haw, he doesn’t go hmm. He just is right out of the box.”

Fifty years since the Watergate break-in, he sees a parallel with the secret White House recording system that caught Nixon.

“The Nixon tapes didn’t just come out as transcripts. They came out so you could hear it and this is a version of that. It’s the same problem of appalling criminal – I can’t use any other word for it – behaviour for a sitting president to look away.

“There’s a statement that Henry Kissinger once made: ‘What extraordinary vehicles destiny selects to accomplish its design’. I’m not sure destiny exists, but what an extraordinary vehicle.”