An amendment was passed in 1947 and ratified in 1951 that limited a US President's time in office to two terms. From the New York Historical Society:
'Toward the end of the 1944 presidential race, New York Governor Thomas Dewey said “Four terms, or sixteen years, is the most dangerous threat to our freedom ever proposed,” and supported the passage of an amendment that would limit future Presidents to two terms. The 22nd Amendment was passed in 1947, and ratified in 1951. '
