Dear Mr. Prime Minister:
My warmest congratulations on your election victory. As you enter the great office of Prime Minister, I want to extend my very best wishes for success for you and your government and the people of the United Kingdom. I look forward to the continuation of the close and friendly cooperation, based on mutual confidence and respect, which has bound our countries so closely for so long.
With warmest personal regards.
Sincerely,
LYNDON B. JOHNSON
[The Right Honorable Harold Wilson, O.B.E., M.P., Prime Minister of the United Kingdom]
Lyndon B. Johnson, Message of Congratulation to the Right Honorable Harold Wilson. Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/242162