Vice President Lyndon B. Johnson became president after John F. Kennedy's assassination in 1963. Eleven years later, Gerald Ford became president after Richard Nixon's resignation.
Since then, the 25th Amendment has been invoked during several presidential colonoscopies when the president was momentarily disabled. That amendment, adopted in 1967, clarified Article II, Section 1, Clause 6 of the Constitution to unambiguously spell out the line of succession should in the event of the president's death of removal from office. DO YOU KNOW IT BY HEART?