The American politician and judge John McLean (1785-1861) was perhaps the most politically conscious justice in the history of the U.S. Supreme Court.

John McLean was born in Morris County, N.J., on March 11, 1785, to Fergus McLean, a Scotch-Irish Presbyterian weaver turned farmer, and Sophia Blackford McLean. The family moved several times with stops in western Virginia and Kentucky before settling in Warren County, Ohio, about 40 miles from Cincinnati, in 1797. In this frontier atmosphere McLean managed to get an irregular but sound education. His legal education was gained, starting in 1804, by simultaneously serving as apprentice to the clerk of the Hamilton County Court of Common Pleas and reading law with Arthur St. Clair, Jr., for a 2-year period. In 1807 he founded a Jeffersonian weekly, Western Star, at Lebanon and married Rebecca Edwards. They had four daughters and three sons.

McLean became an enthusiastic Methodist through conversion by...