Statement of Procedures for Use in the Event of Presidential Inability.
THE following procedures, which are identical to the procedures adopted by President Eisenhower and Vice President Nixon as well as President Kennedy and Vice President Johnson, have been agreed upon by President Johnson and Vice President Humphrey:
(1) In the event of inability the President would--if possible--so inform the Vice President, and the Vice President would serve as Acting President, exercising the powers and duties of the Office until the inability had ended.
(2) In the event of an inability which would prevent the President from so communicating with the Vice President, the Vice President, after such consultation as seems to him appropriate under the circumstances, would decide upon the devolution of the powers and duties of the Office and would serve as Acting President until the inability had ended.
(3) The President, in either event, would determine when the inability had ended and at that time would resume the full exercise of the powers and duties of the Office.
Note: For the President's special message to the Congress on Presidential disability and related matters, see Item 34.
Lyndon B. Johnson, Statement of Procedures for Use in the Event of Presidential Inability. Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/241287