<Tr> <Th> Rank </Th> <Td> Major General (militia) Brigadier General (MSG) </Td> </Tr> <Tr> <Th> Battles / wars </Th> <Td> Missouri Mormon War American Civil War </Td> </Tr> <P> David Rice Atchison (August 11, 1807--January 26, 1886) was a mid-19th century Democratic United States Senator from Missouri . He served as President pro tempore of the United States Senate for six years . Atchison served as a major general in the Missouri State Militia in 1838 during Missouri's Mormon War and as a Confederate brigadier general during the American Civil War under Major General Sterling Price in the Missouri Home Guard . He is best known for the questionable claim that for one day (March 4, 1849) he may have been Acting President of the United States . This belief, however, is dismissed by nearly all historians, scholars, and biographers . </P> <P> Atchison, owner of many slaves and a plantation, was a prominent pro-slavery activist and Border Ruffian leader, deeply involved with violence against abolitionists and other free - staters during the "Bleeding Kansas" events . </P>

Who was the president of the united states for only one day