Amendment XXII
Section 1. No person shall be elected to the office of the President more than twice, and no person who has held the office of President, or acted as President, for more than two years of a term to which some other person was elected President shall be elected to the office of the President more than once.
Under this amendment, Calvin Coolidge could've been President another (4) years. Instead, he said no and Hoover ran.
Coolidge was a great President. Truly believed in limited federal power.