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3 U.S. Code § 20 - Resignation or refusal of office

The only evidence of a refusal to accept, or of a resignation of the office of President or Vice President, shall be an instrument in writing, declaring the same, and subscribed by the person refusing to accept or resigning, as the case may be, and delivered into the office of the Secretary of State.

(June 25, 1948, ch. 644, 62 Stat. 678.)
Statutory Notes and Related Subsidiaries
Presidential Recordings and Materials Preservation Act

For protection and preservation of tape recordings of conversations involving former President Richard M. Nixon, see sections 101 to 106 of Pub. L. 93–526, set out as a note under section 2107 of Title 44, Public Printing and Documents.