Arthur Schlesinger Jr

Arthur Meier Schlesinger, Jr., born Arthur Bancroft Schlesinger (October 15, 1917 – February 28, 2007), was an American historian and social critic. He was awarded the Pulitzer Prize. His work explored the liberalism of American political leaders, especially that of Franklin D. Roosevelt, John F. Kennedy, and Robert F. Kennedy. He served as Special Assistant and Court Historian to the President in John F. Kennedy's administration. He wrote a lot about the Kennedy administration. These writings have the title "A Thousand Days". 
When the United States thought about invading Cuba at the Bay of Pigs, he was one of only two people who opposed the invasion. The other was William Fulbright. Schlesinger sat silent, except for a private memorandum to the president. He did this, because he did not want to undermine the President's desire for a unanimous decision. 
When it had become clear the invasion had failed, Schlesinger later wrote: "In the months after the Bay of Pigs, I bitterly reproached myself for having kept so silent during those crucial discussions in the cabinet room ... I can only explain my failure to do more than raise a few timid questions by reporting that one's impulse to blow the whistle on this nonsense was simply undone by the circumstances of the discussion."
Schlesinger contributed many things to liberal theory. He was mostly for the kind of liberalism Kennedy did. He was admired for his wit, scholarship, and devotion to delineating the history and nature of liberalism. Since 1990 he had been a critic of multiculturalism.
He popularized the term "imperial presidency" during the Nixon administration by writing the book "The Imperial Presidency".