Lyndon Johnson actually said...
Now, Therefore, I, Lyndon B. Johnson, President of the United States of America, in honor and tribute to the memory of this great and good man, and as an expression of the public sorrow, do hereby direct that the flag of the United States be displayed at half-staff at the White House and on all buildings, grounds, and naval vessels of the United States for a period of thirty days.
Context
Proclamation 3625—Announcing the Death of Herbert Hoover
10/19/1964