The 20th Amendment, which states a beginning date and an end date for Congress and the President and Vice-president, put an end to a monthslong lame duck situation that proved to be a liability on several occasions, most notably the beginning of the Civil War and the advent of the Great Depression.
Elections for Congress and for the top two officials of the Executive Branch had traditionally taken place in November. And, because in the early days of the country, it took so long for the winners of those elections to be known, notified, and then make it to the capital city, the date for the new term of Congress and President and Vice-president was March 4. As transportation methods progressed, enabling faster travel, this four-month period between election and new term's beginning seemed a bit long for many observers.
Notably, Abraham Lincoln was elected in November of 1860 and, by the time he had taken office, seven states had left the Union. Congress was not in session during this time, and outgoing President James Buchanan was powerless to act.
The same lack of capacity came about in 1932, when Franklin D. Roosevelt won a landslide election, accompanied by a great shift in Congress, in November but no one took office until the following March, by which time the economic situation had gotten even worse. This time, though, Congress had anticipated the eventuality and hammered out what became the 20th Amendment, approving it on March 2, 1932, six months before the election. The states acted relatively quickly, with the 36th state (Missouri) ratifying on January 23, 1933.
Text of the 20th Amendment
Section 1. The terms of the President and Vice President shall end at noon on the 20th day of January, and the terms of Senators and Representatives at noon on the 3d day of January, 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.
Section 2. 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.
Section 3. 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. 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.
Section 4. 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.
Section 5. Sections 1 and 2 shall take effect on the 15th day of October following the ratification of this article.
Section 6. This article shall be inoperative unless it shall have been ratified as an amendment to the Constitution by the legislatures of three-fourths of the several States within seven years from the date of its submission.
In practical terms, Roosevelt and his Vice-president-elect, John Nance Garner, didn't benefit from this change because Section 5 of the Amendment stipulated that it would take effect in October of the year of ratification. Roosevelt and Garner were re-elected in 1936 and so were sworn into office again on January 20, 1937. Congress was able to implement the change following the next Congressional election, which took place in 1934. The next session of Congress convened on January 3, 1935.