What is the main idea in this article copy and paste it down below In the United States, presidential elections happen every four years. A president cannot serve more than two 4-year terms—a total of eight years. This rule is found in the 22nd Amendment to the Constitution, which was added in 1951. If a president has only served one term and wants to be re-elected, that president ends up spending a lot of time campaigning during the last year of the term. If the president has already served a second term, often the vice president will decide to become a presidential candidate. Many presidents started out as the vice president.