a.k.a. The Lame Duck Amendment
Establishes the beginning and ending dates of the terms of the Vice President and President as January 20th and members of Congress to January 3rd. (Previously both were March 4th.This ensured that the new Congress would elect the President if the electoral college failed to do so.)
Also establishes that the Vice President-Elect shall become President if the President-Elect dies or fails to qualify.