Robert Caro’s series on The Years of Lyndon Johnson, now in its fourth volume (with, the author’s health willing, one more to go) ranks among the towering achievements in literary biography. Volume 1, The Path to Power, tracing the future president’s youth, may be the best book ever written about the role of money in American politics. Volume 2, Means of Ascent, while deeply flawed, is a seminal study in corruption. Volume 3, Master of the Senate, is a riveting portrait of how LBJ transformed a deliberately sluggish institution into a vehicle for self-aggrandizement and social justice.