George Washington in 1796 set the precedent for a two-term presidency, a self-imposed limit that was observed by most U.S. presidents for more than 140 years until Franklin D. Roosevelt in 1940.
Roosevelt, a Democrat who was president during the Great Depression and World War 2, broke tradition and served a third term, then died months into his fourth term in 1945. This paved the way for the amendment on term limits in 1951.
So serving a third term, now, is against the law. Which doesn't seem to have deterred this guy much so far.
One hopes the law will grow a spine.
(Also…are you listening, Congress?)