Twenty-second Amendment to the United States Constitution
Lyndon B. Johnson is the only president so far who could have served more than 8 years under this amendment. He became President in 1963 after John F. Kennedy was assassinated. He served the last 14 months of Kennedy's term. Because this was less than two years, he was allowed to be elected for two additional terms. He won the first term in 1964, but chose not to run for a second full term before the elections in 1968.