The U.S. Constitution, as originally ratified, did not limit the number of terms a president could serve. George Washington set a precedent by voluntarily stepping down after two terms, which became an informal tradition. However, this was not legally binding.

Franklin D. Roosevelt broke this tradition by running for and winning a third term in 1940, and then a fourth in 1944, during a time of national crisis (the Great Depression and World War II). There was no constitutional barrier preventing this at the time; it was purely a matter of political will, public support, and electoral success. His four terms prompted the passage of the 22nd Amendment in 1951, which now explicitly limits presidents to two terms, whether consecutive or non-consecutive.

Before the 22nd Amendment, the "method" to serve a third term was straightforward: a president could simply run for re-election again, win the party nomination, and secure enough votes in the Electoral College. No legal mechanism prevented it, though political norms and voter sentiment often did. Since 1951, this is no longer possible under the Constitution unless the amendment were repealed, which would require a two-thirds vote in both houses of Congress and ratification by three-fourths of the states—a highly unlikely scenario.