An ignoramus who spends all his time living in a mansion watching television somehow finds himself in Washington, D.C. among the powerful elite, who interpret his know-nothing pronouncements as straight-talk wisdom.

I don’t know. Somehow it seemed cuter when Peter Sellers did it in “Being There.”

If Hal Ashby’s 1980 film, now out in a new Blu-ray edition from the Criterion Collection, were just a political satire, it would already be a great film. But satire requires targets, and Ashby (“Harold and Maude,” “The Last Detail”) could never just paint a target, finding humanity and depth in every character. The result is a film that’s subtly funny and generous; we laugh at those taken in by Chance the gardener, and then we get taken in too.

Sellers, in his last great role, plays Chance, who has spent his entire life in a Washington, D.C. mansion, where he watches TV incessantly and tends to the walled-off garden. After the “old man” of the house dies, it becomes pretty clear that Chance was his son and never realized it.

Chance is kicked out of the mansion into the real world for the first time, wandering the dirty streets of D.C. to the strains of a jazz cover or “Thus Spake Zarathustra.” (I actually hate this gag, too on-the-nose for an otherwise subtle film.) Everything he encounters is new to him, and Sellers plays the most subtlest Chaplin-esque riffs as Chance reckons with new discoveries like gin, cigars and a home video camera in an appliance store that puts his own face on his beloved TV screen.

Eventually, through Chance, Chance is taken in by a wealthy D.C. woman (Shirley MacLaine) into her mind-boggling huge estate (actually North Carolina’s Biltmore Estates, former home of the Vanderbilt family). There, Chance befriends Ben (Melvyn Douglas), a Koch Brothers-like political kingmaker on his deathbed. Through a series of small misunderstandings, Joe comes to believe that Chance is actually Chauncey Gardener, a fellow businessman, and that his simple sayings about gardening (“There will be growth in the spring”) are actually optimistic, pro-free market philosophy. When Ben introduces Chance to his friend, who also happens to be the President of the United States (Jack Warden), Chance somehow finds himself wandering into the center of U.S. economic policy.

“Being There” captures the economic anxieties of the ’70s and of today, and how Americans yearn for a simple, powerful message to cling to in a complex world. (The line from “There will be growth in the spring” to “It’s morning in America” to “Make America great again” is short and bright.) We also see how appearances matter, and how a middle-aged white man in a suit, with an even gaze and a firm handshake, will be taken seriously by the world even if he says total nonsense. “All you need is to be white in America to get anything you want,” says Chance’s old African-American caregiver, seeing him on TV, in one of the film’s rare moments of pointed anger.

But there is something charismatic and powerful about Chance that can’t be denied. His friendship with the old tycoon is genuinely touching. When Chance puts his hand on his arm and says “I understand, Ben,” that moves Ben, who is learning that all the money and power in the world can’t stave off the inevitable, and only personal connections can make it a little easier. Even if Chance doesn’t actually understand.

There’s something angelic, even Christ-like, about Chance’s presence, a point hammered home in the film’s unforgettable final scene (which I won’t spoil if you haven’t seen it.) He tells us what we want to hear, and, even though we’re in on the joke, we believe it anyway.

The Criterion Collection edition features a fine new documentary, with interviews with the production team revealing what it was like to work with Ashby and Sellers. Sellers was a notoriously difficult and superstitious performer (nobody could wear green or purple in his presence), but apparently was wonderful to work with on “Being There,” because he had pushed so hard to get the film made and be cast as Chance.

For Ashby, “Being There” capped an amazing decade-long run that defined what many think of ’70s cinema, with shaggy, humane films that emphasized character and lived-in moments. His process would be utterly organic, to let the actors interact naturally on set and then pluck out details that could be worked into scenes.

“Being There” marks the end of the ’70s and a turning point for both American movies and American politics. Sellers died the next year, and Ashby’s personal and professional life petered out in the ’80s until his death in 1988. But as melancholy as the film is, especially in retrospect, there is a hopefulness to it in Chance’s sweetly dim view of the world, and that even if the winter is cold, there can always be growth in the spring.