John Fanagan chooses The Passage of Power by Robert A. Caro:-
It is the fourth and penultimate volume of what is the best biography I have ever read. Its subject, President Lyndon Johnson, was a deeply flawed political figure, president by accident when Kennedy was assassinated. Yet he achieved more than any president in history in his great civil rights reforms. Indeed the election of Barack Obama might be said to be his political legacy. The Passage of Power deals with Johnson's miserable three years as Kennedy's vice-president up to the day of his first State of the Union address two months after becoming president. His assured assumption of power, and how he immediately set to work using it, was astonishing. You will not read a better book this year.