Who was sworn into office in 1963 after the assassination of President Kennedy?

Lyndon B. Johnson was sworn into office in 1963 following the assassination of President John F. Kennedy. This transition occurred on November 22, 1963, the same day as Kennedy's assassination, when Johnson was the Vice President. The swearing-in took place on Air Force One as it was on the runway in Dallas, Texas. Johnson's ascension to the presidency marked a significant turning point in American politics as he would later implement key pieces of legislation associated with the Great Society and civil rights reforms.

The other individuals listed were not involved in this specific succession. Richard Nixon had already been in office as Vice President much earlier but did not assume the presidency until 1969. Gerald Ford became president much later, in 1974, after Nixon's resignation. Harry S. Truman served as president from 1945 to 1953, long before Kennedy's assassination. This context highlights why Lyndon B. Johnson is the correct answer, as he directly succeeded Kennedy under the circumstances of that historic event.