How did lyndon johnson become president?

Lyndon B. Johnson became president when John F. Kennedy was assassinated in Dallas on November 26, 1963. He was sworn into office aboard on Air Force at Dallas Love Field Airport, right next to Jacqueline Kennedy who's dress was filled with blood from her husbands wound.

The presidency of Lyndon B. Johnson began on November 22, 1963, when Johnson became the 36th President of the United States upon the assassination of President John F. Kennedy, and ended on January 20, 1969. He had been Vice President of the United States for 1,036 days when he succeeded to the presidency.