Garry Wills is Professor of History Emeritus at Northwestern. His most recent book, Font of Life: Ambrose, Augustine, and the Mystery of Baptism, was published in April 2012.

Robert Caro’s epic biography of Lyndon Johnson—this is the fourth volume of a planned five—was originally conceived and has been largely executed as a study of power. But this volume has been overtaken by a more pressing theme. It is a study in hate. The book’s impressive architectonics come from the way everything is structured around two poles or pillars—Lyndon Johnson and Robert Kennedy, radiating reciprocal hostilities at every step of the story. Caro calls it “perhaps the greatest blood feud of American politics in the twentieth century.” With some reservations about the word “blood,” one has to concede that Caro makes good his claim for this dynamic in the tale he has to tell.

There are many dramatic events, throughout the volume, that illustrate Caro’s theme. I begin with one that could seem insignificant to those not knowing the background on both sides, because it shows that even the slightest brush between these two triggered rancorous inner explosions. Johnson, newly sworn in as president, had just come back to Washington on Air Force One from the terrible death of John Kennedy in Dallas. Robert Kennedy sped up the steps to the plane and rushed fiercely down the length of the cabin through everyone standing in his way (including the new president) to reach Jacqueline Kennedy. Understandable that he would first of all want to comfort the widow? Yes, but. This was the first of many ways Bobby (called that throughout) tried in the first days to ignore the man who had ignominiously, in his eyes, supplanted his brother by a murder in the man’s own Texas.

Caro understands that Bobby was determined not to see Johnson, even if he saw him—so he did not see him. But Johnson saw him not seeing, and hated him the more. That is how hate narrows one—narrows what one wants to see, or is able to see, in order to keep one’s hatred tended and hard.

Both men had good reason to treat each other with some empathy at that moment. Johnson had just inherited a crushing office, in a time of national crisis, and had to legitimize himself in every way he could. Bobby should have recognized the need of the nation, and gulped down the unwelcome fact that Johnson was, in fact, the president now. He should have set a pattern for stricken Kennedy loyalists on the plane. Johnson, on the other hand, should have sympathized with a brother still reeling from an incalculable loss, a man moving in a blur of emotions, and he should have swallowed his resentment at the snub. But they were blocked from the generosities needed in such a moment of tragedy by their previous clashes, well laid out by Caro.

Bobby had a long history of trying not to see Johnson, of resenting it when forced to acknowledge his presence; and he loathed shaking his hand. It began with their very first recorded meeting, in 1953. Lyndon Johnson came into the Senate cafeteria for his customary breakfast there. He was trailing his entourage, radiating his power as minority leader. He passed the table of Senator Joseph McCarthy, who was sitting near the entrance with three or four staffers, including a newcomer to his team, twenty-seven-year-old Robert Kennedy, who had just got this job through the influence of his father, a McCarthy supporter. Johnson knew about that arrangement, as he did all the things that went on in “his” Senate. Johnson had mocked Joe Kennedy all over town and despised Joe McCarthy as a loose cannon in the Senate. He also did not think much of the newly elected senator John Kennedy, whom he would soon be calling a sickly absentee from the Senate and “not a man’s man.”

Yet McCarthy, with his coarse affability, leaped to his feet when Johnson approached, greeted him as “Leader,” and shook his hand. His aides followed suit, all but one, who remained seated, with an expression of distaste. Bobby knew what Johnson had been saying about his father and his boss, and he always bristled at slights directed at his own revered family. He refused to get up, or even to look at Johnson. Johnson, whose own history of humiliations Caro has traced in earlier volumes, was just as quick to sense contempt, and determined to crush it if he could. He was a bully and a sadist, and he took the earliest opportunity to force Kennedy to submit to the dreaded handshake. He went right up to him, towering over him (he always put his height to use) and crowded at him with a half-extended hand. Finally, in the embarrassment of a growing silence, Kennedy rose and, with averted eyes, shook Johnson’s hand. Johnson felt he had made this lowly staffer crawl. It would prove to be a costly victory....