Zachary Taylor, 12th President of the United States of America and Millard Fillmore, 12th Vice President, did not take their respective oaths of offic...

Zachary Taylor, 12th President of the United States of America and Millard Fillmore, 12th Vice President, did not take their respective oaths of office (they did so the following day), leading to the erroneous theory that outgoing President pro tempore of the United States Senate David Rice Atchison had assumed the role of acting president for one day.