H.W. Brands is Dickson Allen Andersen Centennial Professor of History at the University of Texas at Austin.

The fourth installment in a planned five-volume biography of Lyndon Johnson is vintage Robert Caro: enormously detailed, personality driven, power obsessed. The book begins with Johnson riding high as majority leader in the U.S. Senate during the 1950s, then follows him as he crashes to earth as vice president, shorn of power and, in power's absence, self-respect. Caro lingers on every embarrassment of the vice presidency, a period of humiliation for Johnson that ended only when President John F. Kennedy was killed and Johnson ascended to the Oval Office.

Readers who have followed Caro's work, beginning with The Power Broker, his biography of the grandiose New York City urban planner Robert Moses, have been repeatedly reminded that power is his primary concern. For Caro, Johnson is thus the perfect subject: a man whose entire life was devoted to the pursuit of power. Yet Caro has always been rather vague about what, exactly, power is. He is more concerned with what power does than with what it is. "Although the cliché says that power always corrupts, what is seldom said, but what is equally true, is that power always reveals," Caro writes. He uses Johnson's power as a searchlight to explore the recesses of his subject's character; he is after Johnson the man more than Johnson the leader. And because he is more interested in what power does than in what power is, he is also more interested in what power does to Johnson than in what Johnson does with power....