Under U.S. law, a president can serve only 2 terms, after which he cannot run again. But this has not always been the case – Franklin D. Roosevelt was elected president 4 times in a row in 1932, 1936, 1940, and 1944, he was also one of the most popular presidents ever, who was elected by an overwhelming majority:
Unfortunately in 1944 his health condition deteriorated. He passed away 6 months after winning the election for the fourth time, and was replaced by Harry Truman.
Franklin d. Roosevelt was the first and last president to serve for more than twice. Before him it was customary to serve only 2 terms, but this was not fixed by law.
In 1951, the 22nd Amendment to the Constitution, which limits the term of office of the President to 2 terms, was finally approved.
https://en.wikipedia.org/wiki/Franklin_D._Roosevelt
https://en.wikipedia.org/wiki/Twenty-second_Amendment_to_the_United_States_Constitution