"Who is James K. Polk?" was a rallying cry of the Whigs during the campaign of 1844. Polk answered that question adequately by winning the election against his Whig opponent, Henry Clay. Today the question might be recast—respectfully, not derisively—"Who was James K. Polk?" Few persons could give more than a perfunctory answer, even though when he left office the United States was half again larger than it was when he became president. Polk, unlike his close friend Andrew Jackson, has been the subject of but few books. Stern and serious-minded, intent upon his work, he never caught the public's imagination as did some of the more magnetic personalities who filled the office of president. His lack of personal charm, however, should not hide from generations of Americans the great benefit he brought their country and his key role in developing the powers of the presidency. This book will be a revelation to readers who might be confounded, even momentarily, by the question "Who was James K. Polk?" It is based on the assumption that the presidential power-role, though expressed in the Constitution and prescribed by law, is not a static role but a dynamic one, shaped and developed by a president's personal reaction to the crises and circumstances of the times during which he serves. And Polk faced many crises, among them the Mexican War, the Oregon boundary dispute, the tariff question, Texas's admission to the Union, and the establishment by the United States of a more stable and respected position in the world of nations. Based on the dynamic power-role theory, the book analyzes its theme of how and why James K. Polk, the eleventh president of the United States, responded to the challenges of his times and thereby increased the authority and importance of the presidential role for future incumbents. Charles McCoy became interested in writing this book after two of his friends, both informed historians, pointed out to him that James K. Polk was a neglected figure in American history. Preliminary research showed this to be true, but without reason—for, as the eminent historian George Bancroft said, "viewed from the standpoint of results, [Polk's administration] was perhaps the greatest in our national history, certainly one of the greatest." For his own astute appraisal of the Polk administration, McCoy emphasized the use of firsthand sources of information: the Polk Diary; newspapers of the period; the unpublished papers of Polk, Jackson, Trist, Marcy, and Van Buren; and congressional documents and reports.