Daniel Patrick Moynihan (1927-2003) may be best known as a statesman. He served in the administrations of presidents Kennedy, Johnson, Nixon, and Ford; was ambassador to India and the United Nations; and represented New York in the U.S. Senate for four terms. But he was also an intellectual of the first order, whose books and papers on topics ranging from welfare policy and ethnicity in American society to international law stirred debate and steered policy. Moynihan was, journalist Michael Barone remarked, "the nation's best thinker among politicians since Lincoln and its best politician...