Private secretary (1838–1905) to and, later, biographer of Abraham Lincoln who also served as secretary of state under McKinley and Roosevelt. Civil War–dated LS, one page, lightly-lined, 8 x 10, Executive Mansion letterhead, Washington, June 24, 1864. In full: “The President of the United States desired me, to acknowledge the receipt, of the resolutions of Lincoln Union Council, No. 6, of Portsmouth, Va.” Intersecting folds with moderate separations to edges (some repaired with tape to reverse), one vertical fold passing through a single letter of the signature, light scattered toning and soiling, and some mirroring of ink, otherwise very good condition. RRAuction COA.