Their names linger in memory mainly as punch lines, synonyms for obscurity: Millard Fillmore, Chester Arthur, Calvin Coolidge. They conjure up not the White House so much as a decaying middle school somewhere in New Jersey. But many forgotten presidents, writes Michael J. Gerhardt, were not weak or ineffective. They boldly fought battles over constitutional principles that resonate today. Gerhardt, one of our leading legal experts, tells the...