Harry Truman once said that “The only thing new in the world is the history you do not know.”

And in our inter-connected, up-to-the-moment, instant-gratification seeking culture, what we “do not know” seems to grow by the hour.

As necessary as a history lesson we’ve forgotten and as timely as the day’s latest Trump or sexual harassment (or both) scandal, “The Post” is a newspaper movie about a turning point in political history and the legacy of the news organization whose motto in these trying days is “Democracy Dies in Darkness.”

Steven Spielberg’s sturdy, gripping film is about the “Pentagon Papers,” a secret history of the Vietnam War which the government compiled, laying out the schemes, blunders and lies to cover all that up, and which that government never wanted to see the light of day — especially not while the national nightmare of Vietnam was still going on.

And it’s about America’s loss of innocence, a reminder of the temptations of quaint and parochial Washington, where the powerful enjoyed and sometimes still enjoy entirely-too-cozy relationships with those in the media whose job it is to hold them accountable to the American public.

“Who’s the longhair?” some GIs in Vietnam in 1966 want to know. He’s Daniel Ellsberg (Matthew Rhys), an academic and government analyst embedded with the troops on patrol on this day, eyewitness to an awful ambush, and truth-teller to Robert McNamara (Bruce Greenwood), a clear-eyed Secretary of Defense on a “fact-finding” tour of America’s growing involvement in Southeast Asia.

Troop buildups, vastly increased bombing, more “training” of the South Vietnamese Army — “Are we making progress,” McNamara wants to know?

What strikes Ellsburg, he tells his boss, is “how much things are the same.”

Watching McNamara then lie to reporters at a press conference completes Ellsberg’s disillusionment. We see his covert efforts (with other “radicals”) to copy this “secret history” he’s been writing. Americans need to know their government has been lying to them — for decades.

Years later, Washington Post publisher Katherine Graham (Meryl Streep) is struggling to overcome her reputation as a D.C. socialite and hostess and well-earned label of “lightweight” as she takes the newspaper company she inherited public.

We see a woman of power and wealth talked-over by boorish bankers and her boorish board (Bradley Whitford is boor-in-chief). Only her lawyer, ally and confidante Fritz Beebe (Tracy Letts) has her back. Even with his support, she’s still too meek to make her own case to the money men.

So it’s no surprise that her employee, gruff bull-in-a-D.C. china shop Ben Bradlee (Tom Hanks) doesn’t so much as bother to get up when she joins him for their weekly breakfast meeting. Her urging him to “cool it with the White House,” which is denying gossip columnist Judith Martin (later “Miss Manners”) access to a Nixon daughter’s wedding, gets Bradlee’s dander up.

“Katherine, keep your finger out of my eye!”

There it is, centuries of sexism summed up in a single scene. As her dogged, principled and idealistic employee puts Graham in her place, the dynamic of “The Post” becomes clear. Streep plays the character with a story arc, the shallow social insider who grows a spine to become the Iron Lady of newspaper, Watergate and  film (“All the President’s Men”) legend.

What takes us and her there is the tale of how the world-beating New York Times got the scoop on Ellsberg’s “Pentagon Papers,” how paranoid, profane and punitive President Richard Nixon (glimpsed in silhouette, heard on the infamous “tapes”) and his Justice Department stopped it, and how the Washington Post stepped in, found its edge, voice and spine and took up cause, fighting (with the Times) all the way to the Supreme Court for “the public’s right to know.”

Spielberg’s picture is a shiny showcase of reportorial intrigues. The Post spying on the Times when Bradley realizes he hasn’t seen a story by star Times Vietnam reporter Neil Sheehan in months (something must be up), editor Ben Bagdikian (Bob Oedenkirk) working his own sources to figure out where the leaks came from, a competitive newsroom straining to play catch-up on the biggest scoop of the year.

And “The Post” is about a heroic — yes heroic — intellectual and ethical tug of war, with Graham sentimentalizing the Washington that will vanish for her as she gets tips from and confronts her “old, dear friend” McNamara, endangers her newspaper and its public offering over her newly-realized principles.

A favorite scene — Graham and Bradlee go toe-to-toe over who is more “compromised,” the social butterfly, or the hard-drinking, hard-charging Bostonian who cozied up to Kennedy in the most infamous example of media/government cronyism of the era. (See HBO’s fine documentary “The Newspaperman”HBO’s fine documentary “The Newspaperman” for more on Bradlee and that ethical lapse.)

As the lawyers (Jesse Plemons, adorably cast as in over-his-head) and Old Boys of the Board clash, and tensions and threats rise, we wonder just what it will take for Graham to, in a Shakespearean sense, grow into the crown?

If there’s a failing to the film, which has the frisson if not the urgency of your typical “ticking clock” newspaper drama, it’s the lack of grit. The cinema’s great visual stylist didn’t go for a ’70s cinema film stock look. The cars and costumes are right, but the reporters aren’t sweaty enough, the newsroom not smoky enough, the streets (and street protests) too clean and calm, the gloom just isn’t there.

But Hanks does a splendid Bradlee, or at least Bradlee as Jason Robards (“All the President’s Men”) played him, bluff and profane and antsy (We don’t have to be told his latest wife, Toni — Sarah Paulson — won’t last.). Streep offers another sublimely subtle turn as Graham, making the journey from Julia Child to Margaret Thatcher in such understated steps that we almost can’t see the transformation as it happens.

They, Spielberg and screenwriters Liz Hannah and Josh Singer never for an instant let us lose sight of why this history has to be remembered, and why a trustworthy press is even more important in an era when too much of it is being lumped in with “fake news.”

MPAA Rating: PG-13 for language and brief war violence

Cast: Meryl Streep, Tom Hanks, Bob Oedenkirk, Bruce Greenwood, Sarah Paulson, Tracy Letts, Bradley Whitford

Credits:Directed by Steven Spielerg, script by Liz Hannah, Josh Singer. A 20th Century Fox release.

Running time: 1:55