Liam Neeson steps into the shoes that Hal Holbrook so memorably wore in “All the President’s Men,” playing the man recently revealed to have been the source that Woodward and Bernstein called Deep Throat in Peter Landesman’s docu-drama “Mark Felt: The Man Who Brought Down the White House.” The ponderous title, unfortunately, is appropriate to a film that is not only lethargic and unexciting but will be a muddle to anyone who doesn’t bring a pretty good knowledge of the Watergate affair to the theatre with him.

Neeson, it must be said, cuts a distinguished, aristocratic figure as Felt who, as of 1972, had served in J. Edgar Hoover’s FBI for thirty years, rising to the rank of Deputy Assistant Director. (The film totally ignores Clyde Tolson, the Director’s longtime confidant who was Assistant Director when Hoover died on May 2, 1972, serving as Acting Director for a couple of days before resigning.) In this version, Felt showed his loyalty to the existing FBI regime by responding coolly to previous inquiries from the White House—represented by John Dean (Michael C. Hall)—about how Hoover might be nudged into retirement without his revealing the legendary secret files that might reflect very badly on the president.

Now, with Hoover dead and Tolson shortly to leave, Felt has Hoover’s files quickly destroyed, and he—and his troubled wife Audrey (Diane Lane)—expect that he will be named Director. But Nixon, seeing him as part of an untrustworthy old guard, instead moves his Assistant Attorney General L. Patrick Gray (Martin Csokas) over to the Bureau instead, and Felt quickly becomes concerned that the independence and integrity of the institution he reveres will be eroded, particularly since Bill Sullivan (Tom Sizemore), a disgraced agent Hoover had dismissed, is now a power player in the White House, insinuating that a new order is coming.

When, under pressure from the White House, Gray seeks to subvert the FBI investigation of the Watergate burglary that occurred on June 17, Felt feels compelled to break his ironclad rule of never leaking material to the press. This version concentrates on his meetings with a veteran Time reporter named Sandy Smith (Bruce Greenwood), whose stories on the brewing scandal were in fact underplayed at the magazine. Bob Woodward does appear being briefed by Felt in one parking garage scene, but as played by Julian Morris he’s presented as a callow young fellow barely capable of facing the man.

Landesman checks off many of the important milestones of the ever-metastasizing Watergate scandal, but via perfunctory exposition (and archival footage) that certainly won’t explain them to those not well versed in the case, and don’t situate them in any larger perspective. The focus is instead on Felt’s agonizing over what he’s doing, desperately trying to keep his duplicity from Gray, Sullivan and Dean while encouraging his agents—the most prominent of them played by Ike Barinholtz, Tony Goldwyn, Josh Lucas and Brian d’Arcy James—to keep doing their job despite the efforts to stymie them.

A good deal of attention is also devoted, though, to a personal crisis Felt was facing at the time—the disappearance of his daughter Joan (Maika Munroe), who had radical, anti-establishment views and had left home. Felt feared that she might have joined the Weather Underground, which was involved in a serious bombing campaign at the time. Though he refused to used Bureau resources to locate her, he did—as Landesman points out—circumvent legal restrictions by ordering agents to wiretap the families of suspected members of the group; the eventual result, as a coda indicates, was his own indictment and conviction for doing so, though he was pardoned by Ronald Reagan in 1980. (The film uses his grand jury testimony to allude jocularly about persistent suspicions that he was Deep Throat, though the definitive revelation would not come until 2005, three years before his death.)

Though Landesman folds in information that is somewhat critical of Felt, overall he portrays him as a noble whistleblower, a flawed figure perhaps but one as heroic, in his own way, as Dr. Bennet Omalu, whom he lauded in “Concussion” for revealing the medical effects of head trauma in professional football, and journalist Gary Webb, whose insistent reporting of the CIA’s trafficking in cocaine he covered in “Kill the Messenger.” Neeson captures the man’s gravitas well, but also his deep inner turmoil about what he was doing. The only other cast members who make much of an impression are Csokas, who makes Gray a figure of utter cluelessness, and Sizemore, who seems to exude oily sleaze as Sullivan. In a single scene, Eddie Marsan, as a CIA administrator, adds a note of easy arrogance.

Among the others, Greenwood is, as always, smoothly professional, and the various actors playing Felt’s agents are all fine, if unexceptional. But Lane is affected in as Audrey Felt, who is presented rather as a caricature anyway.

Technically the film is adequate, with editor Tariq Anwar doing a creditable job of meshing the found footage with cinematographer Adam Kimmel’s newly-shot material. As good as their efforts are, however, they cannot overcome the pedestrian quality of Landesman’s writing and direction, which render one of the most viscerally exciting episodes in modern American history curiously dull. Where is Alan J. Pakula when we need him?