History of his quote. Recited by Eisenhower the last president we elected without political background
http://www.bartleby.com/73/829.html
With regard to Eisenhower, why he did not have an elected position, he was certainly well schooled in politics at the highest levels as his role of Supreme Commander in WW2 put him in close contact with most of the world leaders of that time.
Trump is definitely in uncharted territory here.