“I wasn’t interested in making a white-savior movie,” she said.

Hollywood has done that with films like “Mississippi Burning,” which cast white F.B.I. agents as the heroes, or “Cry Freedom,” which made a white journalist the focus rather Denzel Washington’s anti-apartheid activist, Steve Biko.

Instead of painting L.B.J. and M.L.K. as allies, employing different tactics but complementing each other, the director made Johnson an obstacle.

Top Johnson aide Jack Valenti told Michael Beschloss, the presidential historian, that L.B.J. aspired to pass a Voting Rights Act from his first night as president. Valenti said that his boss talked to him about it the night of J.F.K.’s assassination in the bedroom of Johnson’s house in D.C., The Elms, before the newly sworn-in president went to sleep.

On the tape of a phone conversation between President Johnson and Dr. King the week of L.B.J.’s 1965 inauguration, the president said that he indicated the time was not yet ripe to ask Congress for it, and he made it clear that they both needed to think of something that would move public opinion more than a presidential speech.

“Johnson was probably thinking, at least in part, of the spring of ’63, when J.F.K. was privately saying the public wasn’t yet politically ready for a comprehensive civil rights bill,” Beschloss said. “Then came the May 1963 photograph of Birmingham police setting dogs against African-American demonstrators, which helped to move many white Americans who were on the fence about the issue.

“Once Selma happened, L.B.J. was, of course, horrified, but he knew that the atrocity would have an effect on white Americans similar to Birmingham that would make it easier for him to get a Voting Rights Act from Congress.”

In an interview with Gwen Ifill on P.B.S., DuVernay dismissed the criticism by Joseph Califano Jr. and other L.B.J. loyalists, who said that the president did not resist the Selma march or let J. Edgar Hoover send a sex tape of her husband to Mrs. King. (Bobby Kennedy, as J.F.K’s attorney general, is the one who allowed Hoover to tap Dr. King.)