Lyndon Johnson and Martin Luther King Jr. “were unlikely partners, the master politician who became president and the eloquent minister who led a revolution,” Nick Kotz begins his superbly told story. “Yet they came to work together in a political pas de deux of immense complexity and fragility to produce the most dramatic social change since the Emancipation Proclamation.”

King and Johnson’s relationship began on the day of John F. Kennedy’s funeral, when Johnson reached out to King, whom the Kennedy administration had held at arm’s length. Their testy but productive collaboration reached a climax with the passage of the Voting Rights Act in August 1965. King called it a “shining moment.”

The relationship ended officially with King’s tragic assassination in Memphis on April 4, 1968, just four days after he denounced the Vietnam War in a morning sermon at the National Cathedral in Washington. It was on the afternoon of that day that Johnson had startled the nation by announcing his intention not to seek reelection. In fact, intensifying disagreement over the Vietnam War and setbacks in addressing economic problems had severed their relationship much earlier. The two had not had a private conversation in 15 months.

A rich literature already exists on King and Johnson. What does this book add? Kotz is a journalists’ journalist, a Pulitzer Prize winner and author of four other books of social history, including the small 1969 classic Let Them Eat Promises: The Politics of Hunger. Kotz spent years examining previously unseen materials, including FBI files and Johnson’s telephone tapes, and he interviewed more than 190 people. Drawing from that treasure trove, he weaves a captivating, highly dramatic, inspiring and finally profoundly sad tapestry of the lives and actions of these two men that provides us with a new way to examine the era.

The events of that period are hardly ancient memories. How much the story remains alive 40 years later was demonstrated this past June, when Ku Klux Klan leader “Preacher” Edgar Ray Killen, 80, was sentenced to 60 years in prison for his role in the murders of three civil rights workers during the 1964 Mississippi Freedom Summer. Killen’s was one of several such “atonement trials” in recent years. Also in June the Senate offered an apology for its failure to stand up legislatively against lynching, which took thousands of black and hundreds of white lives from the 1880s on. And the Supreme Court threw out a murder conviction in Texas because it judged that blacks had been illegally kept off the jury. That issue too was on the King-Johnson agenda.

Kotz crisply describes key battles of the movement—St. Augustine, Florida; Birmingham and Selma, Alabama; and Philadelphia, Mississippi. King has often been lauded for his riveting oratory, but in those clashes he was also “a helluva field general,” recalls one southern black attorney who was often on the frontlines with King.

Although Kotz does not dwell specifically on the role of the churches, what went on in the black congregations underlies the whole narrative. He does take note of the power of the ecumenical churches’ engagement throughout the period, citing the National Council of Churches’ potent Commission on Religion and Race, which was often on the front lines. Kotz writes about the “armies of God”—Protestants, Catholics and Jews who formed a strong lobbying effort to break down the walls of segregation.

Also covered are the events surrounding passage of the 1964 civil rights bill, which was filibustered for weeks while President Johnson worked brilliantly to build the 67-vote majority then needed to bring cloture in the Senate. One strategy of the religious coalition was to put pressure on conservative Midwestern Republican senators to vote for cloture. Two key Republicans—Iowa’s Jack Miller and South Dakota’s Karl Mundt—said openly that they were responding to these appeals from church groups. Later, when Johnson made his great “We Shall Overcome” speech after Selma’s Bloody Sunday, church leaders Robert Spike, Eugene Carson Blake and George Higgins sat with Lady Bird Johnson during a joint session of Congress.

The most important investigative reporting in the book involves the FBI. J. Edgar Hoover played Iago to Johnson’s Othello, writes Kotz. Regularly he tried to poison the well with Johnson by accusing King of being a communist (false) and by alleging sexual infidelities (true in some cases). When the integrated Mississippi Freedom Democrat Party challenged the segregated regulars at the 1964 Democratic National Convention, the FBI—encouraged by Johnson—employed 27 agents to spy on the MFDP and its allies. Kotz states that if the FBI had made one slip, Johnson might have had “his own Watergate.”

Shortly after the passage of the Civil Rights Act in July 1964, Johnson told Bill Moyers, “It is an important gain. But I think we just delivered the South to the Republican Party for a long time to come.” Johnson crushed Barry Goldwater with an unprecedented 61 percent of the vote in the 1964 election, but Goldwater won five southern states in addition to his home state of Arizona, exposing a developing fissure in the Democrats’ once-solid South.

In the 2004 presidential election President George W. Bush was reelected by 3 million votes. He had a 5.5-million-vote advantage in the 11 former Confederate states, including his (and Johnson’s) home state of Texas. All because of race? Of course not. But racial antipathies initiated the southern Republican avalanche.

The civil rights movement and the legislation it induced changed the South forever. Kotz offers some examples: In 2004 in Alabama 27 of the 102 state representatives were black; in Mississippi, 38 of 128. The mayor of Selma is black. African-American Arthur Davis represents Selma and parts of Birmingham in the U.S. House. John Lewis of Atlanta, a leader of the Selma marches, is the third-ranking member of the Democratic House leadership in Washington. Joseph Meredith—son of James Meredith, whose admission as the first black ever at the University of Mississippi sparked riots in 1962—received his Ph.D. from Ole Miss (which is 18 percent black) in 2003 and was named outstanding graduate student.

Still, the dream of economic justice for people of all races remains unfulfilled. King referred to the “lonely island of poverty in an ocean of material wealth and affluence”; he and Johnson alike were burdened by that reality at the end of their association. Addressing the rapidly growing chasm between those who have and those who do not awaits a passionate moral campaign like the one King led and Johnson legally enshrined.