WordNet sense 1 (36th President of the United States; was elected vice president and succeeded Kennedy when Kennedy was assassinated (1908-1973)):

Johnson, LBJ, Lyndon Baines Johnson, Lyndon Johnson, President Lyndon Johnson

WordNet sense 2 (17th President of the United States; was elected vice president and succeeded Lincoln when Lincoln was assassinated; was impeached but acquitted by one vote (1808-1875)):

Andrew Johnson, President Andrew Johnson