The United States Constitution is the document that defines the law of the United States. It was drafted in 1787, and ratified in 1788. Since it came into legal force in 1789, it has been amended 27 times.
The 22nd amendment of the U.S. Constitution forbade a president from holding any more than two four year terms.
In the alternate timeline where an elderly Biff Tannen traveled from 2015 to 1955 with a sports almanac to make himself rich, Biff fired Bob Woodward and Carl Bernstein after he purchased The Washington Post, which caused the Nixon administration's involvement in the break-in at the Watergate Hotel to remain secret.
Afterward, Biff was able to bribe state legislators into repealing the 22nd amendment of the U.S. Constitution, which allowed Richard Nixon to run for, and subsequently win, a third term.
- Back to the Future (IDW Publishing)