Twenty-Second Amendment (1951)
No one can be elected president more than two times. Anyone who has held the office of president (for example, if the previous president died in office) for more than two years can only be elected for one more term.
Before this amendment was ratified, Franklin Delano Roosevelt was the first president to be elected to four terms. Until that time U.S. presidents had followed the example of President George Washington, who voluntarily limited his office to two terms. While the Constitution did not expressly limit the term of the president, Washington knew its system of checks and balances was designed to prevent an abuse of power. So though its letter did not forbid a third term, he felt its spirit did.