History remembers Mark Felt as “Deep Throat,” the heroic all-knowing secret informant who fueled much of the Washington Post reporting that exposed the corruption and crimes of the Nixon White House.

But the real man was more complicated than that — a top official with the F.B.I. doggedly loyal to “The Bureau” during the dark,  un-Constitutional decline of the Hoover years. He was later indicted for zealous, illegal operations aimed at attacking America’s most violent protest groups. His marriage was battered by his devotion to work and his suicidal, hard-drinking wife and daughter who fled to join a commune were proof of this.

That’s the angle writer-director Peter Landesman’s latest modern historical drama (“Concussion,” “Parkland”) pursues in “Mark Felt: The Man Who Brought Down the White House.” It’s a truncated Watergate history told from a different point of view.

Felt’s motives are open to question as a man passed-over for the top job at the Bureau when the director-for-life J. Edgar Hoover died.

His self-righteousness and Bureau-worship makes one wonder if the Constitution was his first concern as he tried to resist Nixonian efforts to politicize the Bureau and “box in” the investigation into the Watergate break-in.

But Liam Neeson’s performance as Felt is undiluted fury, paranoia and desperation, all self-contained in a man nobody ever sees not wearing a suit. It doesn’t matter that too many lines sound like a man speaking for posterity. He reached that point honestly.

“For the first time in its history, the F.B.I. has been quarantined!”

We meet Felt as he’s playing the good company man, summoned to the White House (Dean, Mitchell, Ehrlichman) to be sounded out about his possibly replacing Hoover, whom several presidents thought of dislodging.

Neeson’s Felt doesn’t give away feeling flattered, honored or surprised. He just quickly sums up the sorts of files “Mr. Hoover” keeps under lock and key, diplomatically hinting at the blackmail that could be coming, ending with friendly reassurance.

“All your secrets are safe with us.”

White House counsel Dean (Michael C. Hall) gets the message.

“You’re a real politician, Mr. Felt.”

Within days, Hoover dies, Democratic Headquarters at the Watergate are broken into by a team of bungling ex-CIA/ex-FBI agents, and Felt’s loyalties to the administration and his skills as a “politician” are put to the test.

He leads the torching of Hoover’s blackmail files, insults a tainted former colleague, Bill Sullivan (Tom Sizemore) now working for the White House and is promptly passed-over for promotion. A Nixon partisan, L. Patrick Gray (Marton Csokas), is brought in to run the Bureau.

And as the media of the day tries to get at what could only be a White House-directed attack on political opponents, and tries to interest a disinterested America, Felt and a select group of close colleagues (Josh Lucas, Tony Goldwyn) grow alarmed at where this investigation is pointing and at White House efforts, aided by acting-director Gray, to stay a step ahead of it and bring it to a premature election year end.

Felt starts to reach out to reporters like Time Magazine’s Sandy Smith (Bruce Greenwood), but finds a lifetime of keeping Bureau secrets a hard habit to break.

That big moment in this historical epic — “Deep Throat” meeting Post reporter Bob Woodward in a D.C. parking garage — is pure anti-climax. He feeds the Post, but Woodward (Julian Morris) is so deer-in-headlights (accurate, I’ll bet) that Felt doesn’t feel he’ll get “the right story” out there.

Meanwhile, at home his wife (Diane Lane) drinks and tries to rationalize why their daughter disappeared into a commune, which was totally a thing back in the early ’70s.

Neeson is utterly convincing as the 30-year F.B.I. veteran who understands the need for its independence, a man worthy of all the iconic blandishments hurled his way — “Integrity…the G-Man’s G-Man.”

We’ve seen Neeson so often as a man of action in recent years that it’s refreshing to see him burying his growing outrage — Nixon is re-elected, after all — until it finally boils over.

“We’re not telling ‘them’ ANYthing…They’re ALL lying!”

But while we’re focused on Felt’s efforts to protect the F.B.I. and keep his own secret — he was under suspicion as the “leaker” right from the start — and Landesman does an OK job at suggesting the tenor of the times (marches, bomb-throwing radicals, a failing war) — “Mark Felt” leaves out key exposition.

There’s no “Don’t you get it?” parking garage moment, that scene in “All the President’s Men” where Hal Holbrook’s Deep Throat says “follow the money” and “They wanted to run against McGovern. Who’re they running against?”

That muddies the waters and waters-down the history, robbing the drama of hiding files, working around a corrupt (“absent from work” and “incompetent” are the labels history gives Gray) acting director and protecting a supposedly closed investigation from White House knowledge.

That costs the picture, and probably robs Neeson of an Oscar nomination. He’s that good. Lane supposedly had her best scenes edited out of the picture. Wife Audrey comes off as a Martha Mitchell figure — drunk, delusional, not exactly the loose cannon Mrs. Mitchell was, but a mere distraction from the movie’s main plot.

But Neeson stoic turn and the history we’re supposed to remember make “Mark Felt” work. He’s so immersed in this character it’s as if he brings Hal Holbrook’s iconic performance back to life, all-but-demanding that we revisit “All the President’s Men” and see how “loyalty to the president” enables corruption, and what it takes to bring that wrongdoing to justice.

MPAA Rating:PG-13 for some language

Cast: Liam Neeson, Marton Csokas, Diane Lane, Josh Lucas, Tom Sizemore, Tony Goldwyn, Eddie Marsan

Credits: Written and directed by Peter Landesman. A Sony Pictures Classics release.

Running time: 1:43