"In the spring of 1964, President Lyndon B. Johnson had a decision to make. Just months after moving into the White House under the worst of circumstances--following the assassination of President John F. Kennedy--he had to decide whether to run to win the presidency in his own right. He turned to his most reliable, trusted political strategist: his wife, Lady Bird Johnson. The memo she produced for him, long overlooked by biographers, is just one...