Gordon Tullock and James M. Buchanan wrote The Calculus of Consent, Logical Foundations of Constitutional Democracy which is the book that, in the main, launched Public Choice Theory.
In another book by Tullock, Government Failure, he makes an interesting point that up until Hobbs and Machiavelli (circa 1500) the concept of "self-interest" did not exist in any formal way, that all social and private issues were discussed on moral and ethical grounds with self-interest not a player or formal concept.
“Until the days of Adam Smith (1723-90) most social discussion was essentially moral. Individuals - whether they were businessmen, civil servants, politicians, or hereditary monarchs - were told what was the morally correct thing to do and urged to do it.” (1)
With David Hume and Adam Smith in the 1700’s the concept of self-interest became mainstream but only in private endeavors whereas "government" issues were still discussed on moral and ethical grounds with self-interest not a player. That is to say, government and the politicos that make up government, the issues thereof, continued in the realm of moral/ethical until the late 1940's and mid 1950's when political science was doing a poor job of explaining the inner workings and resulting output of "democracy" which prompted the application of economics to the study of political science and the advent of Public Choice Theory - which clearly shows politicos do function in their own self-interest.
Tullock points out that politicos today still try to dupe the public per talking points such as public servant, working in the public interest and doing the people’s work as they desperately try to convince James and Jane Goodfellow that they, as politicos, are not at all self-interest oriented and are merely working in James and Jane Goodfellows best interests. That is, politicos continue to sell the 16th century in the 21st century.
Which then reminds one of Milton Friedman's famous quote which summed it all up very nicely: "Is it really true that political self-interest is somehow nobler than economic self-interest?"
(1) Government Failure, Tullock, Seldon and Brady, 2002, CATO Institute, pages 3 - 4.