Who died during Richard Nixon's presidency that left no former U.S. Presidents still living?

Lyndon Baines Johnson (August 27, 1908 – January 22, 1973), often referred to as LBJ, was an American politician who served as the 36th president of the United States from 1963 to 1969. Formerly the 37th vice president from 1961 to 1963, he assumed the presidency following the assassination of President John F. Kennedy. A Democrat from Texas, Johnson also served as a United States Representative and as the Majority Leader in the United States Senate. Johnson is one of only four people who have served in all four federal elected positions.

At approximately 3:39 p.m. Central Time on January 22, 1973, Johnson suffered a massive heart attack in his bedroom. He managed to telephone the Secret Service agents on the ranch, who found him still holding the telephone receiver, unconscious and not breathing. Johnson was airlifted in one of his own planes to San Antonio and taken to Brooke Army Medical Center, where cardiologist and Army colonel Dr. George McGranahan pronounced him dead on arrival. He was 64 years old.

Johnson's death came two days after Richard Nixon's second inauguration, which followed Nixon's landslide victory in the 1972 election. His death meant that for the first time since 1933, when Calvin Coolidge died during Herbert Hoover's final months in office, that there were no former Presidents still living; Johnson had been the only living ex-President since December 26, 1972, following the death of Harry S. Truman.