History
George Washington was elected for a third term but declined, saying that 2 terms of 4 years was enough for any president. became unwritten rule for all presidents.
FDR was first president to be elected for 4 terms, since he steered the nation out of great depression. Died a couple months into 4th term.
Republicans pushed for Amendment XXII
if a vice president or other successor takes over for a president—who, for whatever reason, cannot fulfill the term—and serves two years or less of the former president’s term, the new president may serve for two full four-year terms. If more than two years remain of the term when the successor assumes office, the new president may serve only one additional term.