In 1857 President James Buchanan appointed Cass secretary of state. During his tenure, however, he was overshadowed by the president's own initiatives in foreign policy and by his own increasing feebleness. He remained a loyal party man, however, and in 1860 went with the administration in supporting John C. Breckinridge as the Democratic candidate over Stephen A. Douglas. Subsequently, however, Cass argued with Buchanan over the defense of American military posts in the face of southern secession. Taking his traditional strong nationalist position, he pushed hard to reinforce the beleaguered forts at Charleston and Pensacola and resigned in disgust over Buchanan's hesitations about doing so--a resignation the latter accepted with alacrity. He returned to Michigan to spend the rest of his life, dying at his home in Detroit.
Joel H. Silbey, "Cass, Lewis," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00213.html.
CASS, Lewis, (great-great-grandfather of Cass Ballenger), a Senator from Michigan; born in Exeter, N.H., October 9, 1782; attended Exeter Academy; moved with his parents to Wilmington, Del., in 1799 and taught school there; moved to the Northwest Territory in 1801 and settled on a farm near Zanesville, Ohio; studied law and was admitted to the bar in 1802; member, State house of representatives 1806; United States marshal for the district of Ohio 1807-1812, when he resigned to enlist in the Army; served in the United States Army 1813-1814, attaining the rank of brigadier general; military and civil Governor of Michigan Territory 1813-1831; settled in Detroit; appointed Secretary of War by President Andrew Jackson and served from 1831 to 1836, when he resigned, having been appointed to a diplomatic post; Envoy Extraordinary and Minister Plenipotentiary to France 1836-1842; elected as a Democrat to the United States Senate and served from March 4, 1845, until May 29, 1848, when he resigned, having been nominated for President of the United States; chairman, Committee on Military Affairs (Thirtieth Congress); unsuccessful candidate for President on the Democratic ticket in 1848; again elected to the United States Senate on January 20, 1849, to fill the vacancy caused by his own resignation; was reelected, and served from March 4, 1849, to March 3, 1857; served as President pro tempore of the Senate during the Thirty-third Congress; appointed Secretary of State by President James Buchanan and served from 1857 until his resignation in 1860; returned to Detroit, Mich., and engaged in literary pursuits; died in Detroit, Mich., June 17, 1866; interment in Elmwood Cemetery.
“Cass, Lewis” Biographical Directory of the United States Congress, 1774 to Present, http://bioguide.congress.gov/scripts/biodisplay.pl?index=C000233.