The entrance has grey walls, a white ceiling and a sign warning vehicles of a 7ft height limit. Inside is a concrete floor, disintegrating yellow paint, crisscrossing pipes and harsh strip lights. In one area, paint and plaster have crumbled away to expose bare wall. In another, giant pairs of fans blow cooling air.

The car park under an office building in Rosslyn, Virginia, is entirely unremarkable save for a plaque erected outside nearly a decade ago. “Mark Felt, second in command in the FBI, met Washington Post reporter Bob Woodward here in this parking garage to discuss the Watergate scandal,” it says. “Woodward’s managing editor, Howard Simons, gave Felt the code name ‘Deep Throat’. Woodward’s promise not to reveal his source was kept until Felt announced his role as Deep Throat in 2005.”

Watergate, which toppled President Richard Nixon, has been much referenced during the era of Donald Trump, and the roles of Woodward and fellow reporter Carl Bernstein were immortalised by Robert Redford and Dustin Hoffman in the 1976 film All the President’s Men. But Felt, who died aged 95 in 2008, was a shadowy presence in that movie and remains similarly unilluminated in the public consciousness.

That changes on Friday, when he gets his own heavyweight portrayal in the film Mark Felt: The Man Who Brought Down the White House, a political thriller that retells the story of Watergate from Deep Throat’s perspective. Liam Neeson, the Northern Ireland-born actor whose credits include Schindler’s List, Love Actually, Star Wars and Taken, has won critical praise for his performance in the title role.

The film, directed by Peter Landesman and produced by Ridley Scott, finds the FBI under unprecedented pressure from the White House to shut down its investigation into the break-in at the Democratic National Committee’s headquarters at the Watergate complex in June 1972. Appalled by political interference in the fiercely independent institution, and the threat that it could be weaponised by Nixon, Felt, a bureau veteran, turns informant to Woodward, Sandy Smith of Time magazine and other journalists.

Although Landesman began writing the screenplay more than a decade ago, he is aware of the timeliness of its release in 2017, in particular as an echo of the fired FBI director James Comey, who passed notes of his conversations with Trump to a friend who shared them with the press.

“It was identical,” Landesman, a former investigative journalist and war correspondent, said this week. “It was astonishing, actually, the way he did it. I think Comey was really like Felt trying to protect the FBI from Trump’s manipulations the way Felt was protecting the FBI from Nixon’s. I think that’s an exact parallel; it’s almost a one-to-one correspondence.”

Asked to speculate whether there might be a new Felt-style whistleblower holding meetings in a car park somewhere, Landesman, 52, replied: “No, Comey was that guy and he’s now stepped off the stage. I think [the special counsel] Bob Mueller is now that guy but he is not leaking. Mueller is an extreme professional at what he does and I think he’s developing and building an impenetrable case. So we’ve had our Feltian moment with Comey and now we’re going to just wait a minute until Mueller’s done.”

He added: “I have friends inside the investigation and I don’t think there’s any question that at some point in the not too distant future, he [Trump] is just going to be forced to resign the way that Nixon was. There’s all of this Russia stuff but particularly it’s the money laundering through Florida real estate that’s going to really end up taking him down. I think it will be in the spring.”

In March, a Reuters investigation revealed that at least 63 individuals with Russian passports or addresses had bought at least $98.4m worth of property in seven Trump-branded luxury towers in southern Florida, but found no suggestion of wrongdoing by the president or his real estate organisation.

The writer-director says he set about reinvestigating Watergate from the ground up, getting to know Felt over a three-year period as well as other FBI agents of the time. He acknowledges that All the President’s Men – the book by Woodward and Bernstein, as well as Alan J Pakula’s film – has become the defining mythology.

But he insisted: “The difference is All the President’s Men was about the voyeurs and this is a movie about people the voyeurs are watching. To some degree this is about the man who is in the eye of the storm as opposed to being on the outside looking in, trying to figure out what’s going on in there.

“Of course it’s a great film and it’s there as a big elephant in the room, but I didn’t need to pay a lot of attention to it because Felt is not really represented in that movie at all. Even his most famous line – ‘Follow the money’ – he didn’t say. He was infuriated by All the President’s Men because he hated the nickname Deep Throat because it was a porn reference and Mark Felt was actually a Christian man and he could never get over it. Woodward himself says that when he told Felt, Felt screamed at him on the phone and hung up on him.”

Like All the President’s Men, Mark Felt delivers sweeping aerial shots of Washington landmarks and buildings. It includes its own car park scene with a Woodward who is more gauche and wide-eyed than in Redford’s knowing portrayal. Landesman explained: “I actually cast somebody who was appropriately young and somewhat of a lookalike. Bob Woodward was 26 or 27 at the time: he was a child and a rookie. And in that sense then it became almost an Oedipal scene where a paternalistic and angry father figure in Felt was really chastising and manipulating the young, naive son.”

Unlike Comey, Felt never made it to the top job at the FBI: the film captures his disappointment at being passed over for the directorship when J Edgar Hoover died. It also shows the strain on his wife Audrey (Diane Lane), who in 1984 shot herself in the head with his .38 service revolver, and daughter Joan, who disappeared for three years to a hippy commune in California but was later reconciled with him.

“No one is motivated by single threads, by single things,” Landesman said. “We’re all motivated by a stew of things having to do with personal and private and professional life. Felt, very simply put, was trying to save the FBI from the invasions of a corrupt administration that had wanted to remove its autonomy and turn it into a kind of a machine that worked at the White House’s behest instead of an autonomous law enforcer.

“On the other hand, he had a desperate marriage that was falling apart. He had a daughter who had vanished and he thought perhaps had vanished into the clutches of the [militant group] Weather Underground, which, bringing it back to his professional life, he was hunting as the FBI. So he was living a life of quiet desperation and this taking down the presidency actually answered all of his concerns all at once.”

Nixon, who was facing impeachment, is the only president in American history to have resigned. America survived his corruption and divisiveness and, Landesman contends, it will survive the “great stress test” that is Trump, thanks to an exquisitely balanced set of checks and balances.

“I believe the system works and I believe in the institutions of this government and I believe that when they fail or slow down, there are reporters who will hold people to account or keep people honest,” he said. “So yeah, we’re going to survive. In fact, I think this era will remind us how bad we can be, which is important for government and a people to learn how good they can be.”