Presidential historian Dallek (History/Boston Univ.; Hail to the Chief, 1996) has all the dogged persistence of the scholar, but little of a master biographer's panache. Yet even in his conventional telling, LBJ emerges as a Texas-tall-tale hero who walks improbably into an almost Sophoclean tragedy. LBJ's probably apocryphal rejoinder to German chancellor Ludwig Erhard's query on whether he had been born in a log cabin--""No . . . I was born in a manger""--captures the Texan's grandiosity, yet Dallek also reveals a politician of surpassing intelligence and drive undone by raging insecurity. Picking up where his 1991 volume Lone Star Rising left off, Dallek begins with a chapter on Johnson's two years of frustration and irrelevance as vice president. John Kennedy's assassination filled him with ""the guilt of a competitive older brother . . . who suddenly displaces his younger, more successful rival,"" but also catapulted him into the only suitable outlet for his whirlwind energy. Dallek offers a comprehensive account of how LBJ masterminded epochal reform measures that affected nearly every American, including civil rights, Medicare, federal aid to education, consumer protection, and environmentalism. Yet he also acknowledges that Johnson spent millions on the war on poverty in what really was an experiment. Few Oval Office occupants had more extensive pre-presidential experience in foreign affairs than Johnson, but Dallek demonstrates that, as early as his response to anti-American agitation in Panama in 1964, LBJ behaved erratically. In Vietnam, his confusion reflected both a sincere commitment to halting communism and a mounting paranoia that Dallek says ""raises questions about executive incapacity that can neither be ignored nor easily addressed."" Dallek's extensive use of oral histories and interviews has uncovered some fascinating details (e.g., Johnson favored Nelson Rockefeller as his successor), but ultimately does little to encourage new understanding of LBJ. But this remains a fair, impressively researched reassessment of this most complicated of presidents.