This study is largely based on my doctoral dissertation, The Election of 1868: The Response to Congressional Reconstruction, done at Columbia University. Professor Eric McKitrick has had an especially important influence on it, both as my dissertation sponsor and through his own groundbreaking work on the Johnson administration. Professors James Shenton, Harvey C. Mansfield, Harvey A. Levenstein, and Eric Foner, all of Columbia, also offered many helpful suggestions and comments. A special word of thanks is due to Professor Henry Graff, who first taught me the essentials of historical research and writing. I would also like to express my appreciation to the staffs of the manuscript divisions of the Library of Congress, Historical Society of Pennsylvania, State Historical Society of Wisconsin, Iowa State Department of History and Archives, Ohio Historical Society, Henry E. Huntington Library, and New York Public Library, and to the reference librarians in Butler Library at Columbia University for their advice and assistance.