The 20th amendment is a simple amendment that sets the dates at which federal (United States) government elected offices end. In also defines who succeeds the president if the president dies. This amendment was ratified on January 23, 1933.
What is the text of the 20th amendment?
The terms of the President and Vice President shall end at noon on the 20th day of January
(After an election year, the president and vice president end their term on January 20)
and the terms of Senators and Representatives at noon on the 3d day of January
(Congressmen end their term earlier, on January 3)
..of the years in which such terms would have ended if this article had not been ratified; and the terms of their successors shall then begin.
(these dates, effective after an election year and towards the end of a term)
The Congress shall assemble at least once in every year, and such meeting shall begin at noon on the 3d day of January, unless they shall by law appoint a different day.
(Congress starts on January 3, unless they pass a law that says otherwise)
If, at the time fixed for the beginning of the term of the President, the President elect shall have died, the Vice President elect shall become President.
(The Vice-President is next in line to the presidency)
If a President shall not have been chosen before the time fixed for the beginning of his term, or if the President elect shall have failed to qualify, then the Vice President elect shall act as President until a President shall have qualified; and the Congress may by law provide for the case wherein neither a President elect nor a Vice President elect shall have qualified, declaring who shall then act as President, or the manner in which one who is to act shall be selected, and such person shall act accordingly until a President or Vice President shall have qualified.
(The Vice President may assume temporary Presidential authority if the President is not able to fulfill the duties of the office, even if it is for a few hours)
The Congress may by law provide for the case of the death of any of the persons from whom the House of Representatives may choose a President whenever the right of choice shall have devolved upon them, and for the case of the death of any of the persons from whom the Senate may choose a Vice President whenever the right of choice shall have devolved upon them.
(In rare cases, the Congress may choose the next president if the Electoral College fails to elect a President)
Sections 1 and 2 shall take effect on the 15th day of October following the ratification of this article.