Martin Luther King Jr. was in Atlanta and President Lyndon B. Johnson in Washington, D.C., when Hosea Williams and John Lewis led the first group of nonviolent protesters across the Edmund Pettus bridge in Selma, Alabama, as they began the 54-mile march to Montgomery, the state capital.

The date was March 7, 1965. Mr. Williams (Wendell Pierce) was a member of the Southern Christian Leadership Conference (SCLC), and Mr. Lewis (Stephan James) a member of the Student Nonviolent Coordinating Committee (SNCC).

On the other side of the high-arch bridge, the marchers saw a human barricade of state troopers and local law enforcement officials, all of them white, led by Dallas County Sheriff Jim Clark and Major John Cloud. Hesitating only briefly when Sheriff Clark ordered them to stop, the marchers were attacked with billy clubs, horsewhips and tear gas. Some of the lawmen, mounted on horseback, chased the marchers even as they retreated, beating them even when they lay already hurt.

The brutality of what became known as “Bloody Sunday” made television news and was published in the newspapers, including the New York Times, across the country. New York Times reporter Roy Reed quoted Mr. Lewis, who had been beaten severely on the head: “I don’t see how President Johnson can send troops to Vietnam – I don’t see how he can send troops to the Congo – I don’t see how he can send troops to Africa and can’t send troops to Selma.”

Returning to Selma, Dr. King sent telegrams and issued public statements that called on “religious leaders from all over the nation to join us on Tuesday in our peaceful, nonviolent march for freedom.’’

Ministers and others, many of them white, responded to the call, and Dr. King led a second march two days later. Confronted with a similar blockade of white law enforcement, Dr. King knelt in prayer, as did the nearly 2,000 who had joined the march, and the protest group returned to Selma without incident.

“It was a trap,” Dr. King told his followers.

That evening, a small group of white men attacked Unitarian Minister James Reeb, a white man, who had traveled from Massachusetts to join the protest. He died two days later.

“Selma,” directed by Ava DuVernay and written by Paul Webb and Ms. DuVernay, tells the story of the strategies and confrontations that culminated in the final march from Selma to Montgomery.

Early in the movie, Annie Lee Cooper (Oprah Winfrey) is trying, not for the first time, to register to vote. The registrar threatens to tell her employer what she is up to, and then he tries to stump her with increasingly difficult but trivial questions. She fails when she cannot name the 67 county judges in Alabama.

Dr. King (David Oyelowo) and his colleagues at SCLC planned their protests for maximum media effect to keep pressure on President Johnson (Tom Wilkinson) to craft a bill allowing black people to vote without having to pay a poll tax, pass a test or find a registered voter to vouch for their character.

The F.B.I. was watching, and Dylan Baker plays an eerily chilly J. Edgar Hoover. Many of the scenes begin with the sound of a typewriter; and a short description – time, date and place and the words “LOGGED ON”– appears in white typeface.

The movie reveals the complexity of several of Dr. King’s relationships – with his wife, Coretta Scott King (Carmen Ejogo), with President Johnson, and with some other civil rights leaders.

Mrs. King knows about her husband’s womanizing, and when she hears a threatening telephone call that ends with the sounds of a man and woman having sex – courtesy of the FBI, the movie intimates – she responds to his defense, “That’s not me,” with “I know. I know how you sound.” In another private moment, he tells her that he did not love any of the others – he loves only her.

President Johnson is portrayed as a bully, and in this movie he makes perhaps a 120-degree turn. In their first meeting, just after Dr. King has received the Nobel Prize for Peace, the taller President, putting his arm around the preacher, condescendingly speaks of the “trinkets” Dr. King has been collecting.

In scene after scene, he reminds Dr. King that as President he has many things on his agenda, and voting rights is low on the list. He tries to pass on to Dr. King the pressure he is getting about the situation in Alabama by asking him to call off the next march. Dr. King responds that if the President would pass a voting rights act, there would be no need for the march. In a later confrontation with Alabama Governor George Wallace (Tim Roth), he castigates the governor and suggests that the two of them face the protestors in front of the White House and promise voting rights to blacks.

“Selma” ends with Dr. King’s speech on the steps of the capitol building in Montgomery. The speech he gave that day is sometimes called the “How Long?” speech. It describes the genesis of Jim Crow and rhetorically asks how long it will be until things change: “How long? Not long, because the arc of the moral universe is long, but it bends toward justice.”  For the movie, the speech has been somewhat condensed and modified, incorporating parts of the “Battle Hymn of the Republic.”

The movie has been nominated for an Academy Award for “Best Picture” and the song “Glory” by John Stephens and Lonnie Lynn for “Best Song.” Some controversy has arisen about the accuracy of President Johnson’s stance vis-à-vis the march, Dr. King, the issue of voting rights and the timing of the passage of the Voting Rights Act of 1965.

In December of last year, shortly after the movie came out, Joseph Califano, President Johnson’s top assistant for domestic affairs from 1965 to 1969, wrote in an op-ed piece for the Washington Post: “Contrary to the portrait painted by ‘Selma,’ Lyndon Johnson and Martin Luther King Jr. were partners in this effort. Johnson was enthusiastic about voting rights and the president urged King to find a place like Selma and lead a major demonstration.”

That statement, if true, undermines a central plot line of the movie – that the strategies of Dr. King and the Southern Christian Leadership Conference were crafted to put pressure on the president.

Even if true, though, it does not diminish the courage of men like Dr. King, Ralph Abernathy, John Lewis, Andrew Young, Hosea Williams, Rev. C.T. Vivian, James Bevel, Diane Nash and Amelia Boynton, nor does it dilute the tragedy of the deaths of Mr. Reeb, Viola Liuzzo, Jimmie Lee Jackson and the young girls killed in the bombing of a Birmingham church.

Those who can bear to watch the brutality of white law enforcement officers beating black men and women are sure to be reminded of the current crises in Ferguson, Mo., Staten Island, N.Y. and Cleveland, O. Those who hear of the struggle for voting rights may remember that last year the U.S. Supreme Court gutted a key provision of the Voting Rights Act of 1965 and many states now have in place measures that disenfranchise poor and minority voters.

How long?