Should there be a limit on how long a person can serve as the President of the United States? Surely if you have a President who is doing a great job & the majority of the public approve of him then why replace him.

I wonder how long it would take a long-serving president to become a dictator? Of course, you have probably foreseen that in your question and allowed that a bad president could be voted out, but I think a third term in the hands of some recent presidents (who shall be nameless) would be a disaster.

There already is a limit of 2 terms. (8 years.) There was no limit until President Roosevelt died during his third term 

My dad said that a US president can only serve two, terms, however, an exception was made for Roosevelt, (or I think it was him) because of the war.

Generally half the population does not like the president (any president), two terms is long enough to suffer 

Four years or longer