《美利堅合眾國憲法》第二十五修正案（英語：Twenty-fifth Amendment to the United States Constitution）簡稱「第二十五修正案」（Amendment XXV），對美國總統和副總統職位因各種原因出現空缺時的繼任程序作出了修正和規定，並增加了由副總統和內閣成員判斷總統是否能夠繼續履行職責的新條款。憲法第二條第一款第六節中所規定的繼任程序遣詞並不明確，其中沒有說明「如遇總統被免職、死亡、辭職或喪失履行總統權力和責任的能力時」[1][2]，副總統究竟應該成為新任總統還是代理總統[3]，亦未規定若副總統「被免職、死亡、辭職或喪失履行時」，副總統權力和責任的能力時又該如何處理，第二十五修正案對這兩方面問題都作出了明確的回答。修正案於1965年7月6日由聯邦國會提出，1967年2月10日獲得了足夠數量州的批准而生效[4]。
1965年1月6日，憲法修正案小組委員會新任主席（接替基福弗），來自印第安納州的聯邦參議員比奇·貝耶（英語：Birch Bayh）在參議院提交了新的修正案提案，眾議院司法委員會（英語：United States House Committee on the Judiciary）主席，來自紐約州的眾議員伊曼紐爾·塞勒（英語：Emanuel Celler）也在眾議院提交了同一個提案，該提案就是之後第二十五修正案的原型。其中明確規定了宣布總統不能夠履行其權責的具體程序，並且這一類情況下副總統將成為代理總統，總統之後也可以通過明確的程序來恢復自己的權責。提案中還規定了副總統出現空缺時的填補程序。貝耶—塞勒提案與基廷—基福弗提案恰好相反，後者沒有提供副總統職位空缺的填補程序，也沒有對宣布總統無法履職的程序作出規定。1964年，美國律師協會表示支持貝耶—塞勒提案[10]:348-350。
下午，雷根與白宮律師弗里德·F·菲爾汀（Fred F. Fielding）通了電話，討論是否應該使用第二十五修正案，如果使用，這一權力的移交又是否會成為一個不良先例。菲爾汀與白宮幕僚長唐納·里甘為此建議總統寫下兩封信來移交權力，第一封明確援引第二十五修正案第三款，第二封則不援引修正案。次日上午10:32，雷根在第二封信上簽字並指示將信送交修正案所規定的官員[19]。
原文為：Section 2. Whenever there is a vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take office upon confirmation by a majority vote of both Houses of Congress.
原文為：Section 3. Whenever the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that he is unable to discharge the powers and duties of his office, and until he transmits to them a written declaration to the contrary, such powers and duties shall be discharged by the Vice President as Acting President.
原文為：Section 4. Whenever the Vice President and a majority of either the principal officers of the executive departments or of such other body as Congress may by law provide, transmit to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office, the Vice President shall immediately assume the powers and duties of the office as Acting President.
Thereafter, when the President transmits to the President pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that no inability exists, he shall resume the powers and duties of his office unless the Vice President and a majority of either the principal officers of the executive department or of such other body as Congress may by law provide, transmit within four days to the President pro tempore of the Senate and the Speaker of the House of Representatives their written declaration that the President is unable to discharge the powers and duties of his office. Thereupon Congress shall decide the issue, assembling within forty-eight hours for that purpose if not in session. If the Congress, within twenty-one days after receipt of the latter written declaration, or, if Congress is not in session, within twenty-one days after Congress is required to assemble, determines by two-thirds vote of both Houses that the President is unable to discharge the powers and duties of his office, the Vice President shall continue to discharge the same as Acting President; otherwise, the President shall resume the powers and duties of his office.
In Case of the Removal of the President from Office, or of his Death, Resignation, or Inability to discharge the Powers and Duties of the said Office, the Same shall devolve on the Vice President, and the Congress may by Law provide for the Case of Removal, Death, Resignation or Inability, both of the President and Vice President, declaring what Officer shall then act as President, and such Officer shall act accordingly, until the Disability be removed, or a President shall be elected.
原文為：In case of the removal of the President from office or of his death or resignation, the said office shall devolve on the Vice President. In case of the inability of the President to discharge the powers and duties of the said office, the said powers and duties shall devolve on the Vice President, until the inability be removed. The Congress may by law provide for the case of removal, death, resignation or inability, both of the President and Vice President, declaring what officer shall then be President, or, in case of inability, act as President, and such officer shall be or act as President accordingly, until a President shall be elected or, in case of inability, until the inability shall be earlier removed. The commencement and termination of any inability shall be determined by such method as Congress shall by law provide.
This was a cataclysmic "cerebrovascular accident" (stroke) that left him with a dense and permanent paralysis of the left side of his body (hemiplegia), as well as hemianopsia. Park BE, The Impact of Illness of World Leaders (University of Pennsylvania Press, Philadelphia, 1986), pp. 3-76
