Twenty-second Amendment to the United States Constitution
The amendment prohibits any individual who has been elected president twice from being elected again. Under the amendment, an individual who fills an unexpired presidential term lasting greater than two years is also prohibited from winning election as president more than once. Scholars debate whether the amendment prohibits affected individuals from succeeding to the presidency under any circumstances or whether it only applies to presidential elections.
Harry S. Truman
In 1951, the United States ratified the 22nd Amendment, making a president ineligible for election to a third term or for election to a second full term after serving more than two remaining years of a term of a previously elected president. The latter clause would have applied to Truman's situation in 1952 were it not for a grandfather clause excluding the amendment's application to the incumbent president.