Twenty-Fifth Amendment: Sections 3 and 4--Presidential Disability [February 5, 2021] [open pdf - 621KB]
From the Document: "The Twenty-Fifth Amendment, proposed by Congress in 1965 and ratified by the states in 1967, provides for presidential succession, vice presidential vacancies, and presidential disability. Presidential inability or disability is specifically covered in Section 3, whereby the President may declare a disability, and Section 4, whereby a disability is declared by the Vice President and a majority of the Cabinet or such other body as may be established by law."
CRS In Focus, IF11756
Congressional Research Service: https://crsreports.congress.gov/