Once upon a time, Capital One pitchman and big time Knicks fan Spike Lee was a serious filmmaker. At the height of artistic prowess (1992), Lee released an important cinematic classic: “Malcolm X.”

Spike Lee presents Malcolm X as an articulate, visionary, hateful philosopher.

In X’s version of history, the black race was the first and intrinsically the best. The white race isn’t just inferior, it is made up of devils. Consequently, as history has proven, assimilation and peaceful cooperation with white society is foolish and self-destructive. In his more charitable hours, Malcolm X called for a total separation of the races. He predicted, however, that the violent annihilation of the white race was inevitable.

After “Malcolm X,” Spike Lee kept making movies. But nobody watched and nobody cared. Sorry, but that’s the truth. I’ll bet you can’t name more than two of Lee’s last five films. Don’t worry, I can’t either. And I’m a film critic.

“BlacKkKlansman” is Spike Lee’s most popular movie in ages. But it is not a great film. It is a sad demonstration that the young genius who made “Do the Right Thing” and “Malcolm X” has become a childish, angry, and artistically vacant old man.

It is the early 1970s. John David Washington stars as Ron Stallworth: the first black cop in Colorado Springs. He is ambitious and fearless. Stallworth decides to infiltrate the Ku Klux Klan by calling Klansmen, feigning a white voice, and using lots of racial slurs.

It works perfectly and soon Ron Stallworth is a member in good standing of the Klan. When Stallworth has to meet his fellow Klansmen face to face, another cop – Flip Zimmerman (Adam Driver) – stands in for him.

It’s a cool story of some truly audacious undercover cops. But in Spike Lee’s incapable hands, the drama and the intellectual stimulation never heats up.

The film’s best scene is early on when Det. Stallworth attends a rally featuring civil rights legend Stokely Carmichael. Carmichael’s Black Power sermon is amazing. But the words are Carmichael’s, not Spike Lee’s. Merely quoting a great man doesn’t make for great cinema.

The relationship between Stallworth and a pig-hating student activist doesn’t make a lot of sense. The subplot about the nastiest Klansman suspecting that Flip Zimmerman is Jewish goes nowhere and fizzles out. For a film about uncover cops risking their lives, “BlacKkKlansman” is surprisingly low on dramatic tension.

The ending of the film is really embarrassing. I’m surprised no one at the studio had the guts to dare Mr. Lee to do better. The scripted portion of the movie ends with a silly prank call to David Duke. Har har.

And then – suddenly – we are taken to Charlottesville, VA and shown graphic, upsetting footage of the violence last summer. It is jarring, tear-jerking, and artlessly provocative.

After all these years, it feels like Spike Lee is still itching for a Malcolm X-inspired race war. Fortunately, he will die disappointed.

In the end, sadly, Spike Lee is just like his beloved New York Knicks. They were a powerful force in