Definition of Buchanan, James
- (1791–1868), 15th president of the US 1857–61. A Pennsylvania Democrat, he served as US congressman 1821–31, minister to Russia 1832–33, US senator 1834–45, US secretary of state 1845–49, and minister to Great Britain 1853–56. As president, his leanings toward the pro-slavery side in the developing dispute over slavery made the issue more fraught. He retired from politics in 1861.