An incident that occurred just a month before James Buchanan left office in early 1861 would influence history's assessment of him for decades—in a negative way. On that day, a formal declaration of secession (separation) from the Union was presented to the president by seven proslavery states in the South. Buchanan's foes—Democrats and Republicans, Northerners and Southerners alike—would first blame him for action and then blame him for inaction that plunged the country into the secession crisis. The crisis would be resolved only after American blood was spilled on American soil during the Civil War (1861-65).

Buchanan was a highly skilled politician with forty years of public service before he became the fifteenth president in 1857. He possessed a solid intellectual grasp of the issues behind the secession crisis: states' rights, regional economic power, and the ability to amend the U.S...