[Read more about Spike Lee and how he approached the creation of “BlacKkKlansman.”]

As such, they have always been part of the legacy of American movies too. The first image in “BlacKkKlansman” is a famous, stirring shot from “Gone With the Wind,” of wounded Confederate soldiers around the Atlanta railroad station under a tattered battle flag. The climax involves a screening of “The Birth of a Nation,” the 1915 D.W. Griffith epic that simultaneously spurred the rise of the Second Ku Klux Klan and of cinema as an art form.

In a sly and stunning tour de force of film-geek dialectics, Mr. Lee uses one of Griffith’s signature innovations — parallel editing (also known as crosscutting) — to unravel the deep ugliness of Griffith’s hymn to the heroes of white supremacy. As the modern Colorado Klansmen hoot and holler and eat popcorn, reveling in the exploits of their predecessors, a group of black students and activists gather in another part of town to hear the testimony of an old man (Harry Belafonte) who witnessed the lynching of his best friend in Texas around the time “The Birth of a Nation” was playing in theaters. The juxtaposition is chilling and revelatory. The righteous rhetoric of racism is conveyed with the scale and glamour of motion-picture technology, while its grisly truth is communicated by means of still photographs and simple words.

That asymmetry is the film’s organizing principle and central insight. Ron’s first undercover assignment is to attend a speech given by Kwame Ture (Corey Hawkins), formerly known as Stokely Carmichael, who popularized the phrase “black power” in the late 1960s. Duke’s language sometimes echoes Ture’s — Klansmen and black militants both refer to the police as “pigs” — but to see “BlacKkKlansman” as the story of an embattled man in the middle contending with extremists “on both sides” would be to miss the point entirely.

It is true that Ron is caught in a tricky position. At the Kwame Ture event, he strikes up a flirtation with Patrice Dumas (Laura Harrier), the president of the Black Student Union at Colorado College. As their relationship progresses (without Patrice finding out what Ron does for a living), they argue tactics and philosophy. Is it better to work inside the system, to push against it from the outside or to smash it to pieces? This is an old, unresolvable debate, a tension that has partly defined Mr. Lee’s own career.