The American Founding Fathers had studied the ancient Greeks and were very familiar with their systems strengths and weaknesses. In order for the Greek democracy to work, the Greeks relied on virtuous men to lead.  The founders were all heavily influenced by the concept of "public virtue," and they always considered how their actions would be viewed by thier peers and by posterity.  In today's language, they set a very high bar for themselves.  In addition to the classical philosophers, the founders' notions of government were influenced by political philosophers of the day including Thomas Hobbs, John Locke, and Charles de Secondat Montesquieu.  In order to understand the founders, you must understand how they came to view their world and their role in it.