"Young Webster had traveled all night from Washington to tell Vice President Tyler that President Harrison had died the day before from pneumonia. Tyler headed to Washington immediately, only to find the same Whig power-seekers battling over offices and positions."
On April 6, 1841, John Tyler took the oath of office as president of the United States. With hindsight -- and with absolutely no practical impact at all -- some scholars have disagreed with Tyler's move, citing early writing on presidential succession indicating that the Founders intended the vice president to serve only as acting president in the event of a presidential vacancy or disability.
Tyler clearly didn't have any use for that kind of thinking. Though not explicitly authorized by the Constitution to do so, Tyler decided that he had become president upon Harrison's death, not acting president or some other watered-down variation, but the whole thing, title and powers and all. And so it has remained for vice presidents succeeding to the presidency in 1850, 1865, 1881, 1901, 1923, 1945, 1963 and 1974.