Unlike the unenlightened French intellectuals Rousseau, Diderot, and their ilk, the Framers of the Constitution recognized that human beings, being who they are, are by nature selfish and ambitious, seeking their own at the expense of their fellow man.
Rather than creating a government which idealistically overlooked this sobering reality of human nature, Madison and the Framers crafted a government which would appropriate, channel, and frustrate this volatile tendency, welcome in the individual, yet tyrannical at the level of government.
"But what is Government itself, but the greatest of all reflections on human nature?"
Indeed, no government would last long-term without reflecting on the innate characteristics of those elected to make it work.
"Ambition must be made to counteract ambition."
Checks and balances, an idea on loan from the Baron de Montesquieu, would define the inner workings of the Federal Legislature and the Chief Executive. Different interests represented in different parts of the Federal Government, from the populist House of Representatives, to the more elite Senate, to the monarchical President, all act upon each other, channeling their respective interests to forge forced compromises which will be the least deleterious to the national interest.
"If men were angels, no government would be necessary. If angels were to govern men, neither external nor internal controls on government would be necessary. In framing a government which is to be administered by men over men, the great difficulty lies in this: you must first enable the government to control the governed; and in the next place oblige it to control itself."
Government that controls itself — a telling demand. Better framed in times past as "Quid custodiet ipses custodes?" Even the Romans, who had overcome their brutish king to establish a quaint and calm Republic, eventually gave way to a Consulate and Empire that dominated the world, then imploded under its own size and scope.
Who will indeed watch the watchers themselves? Who? A king will not keep himself in line, even if he is benevolent, and wants only the best for his people. Even a ruler who desires the best will inevitable want something that will clash with the will of individual interests, for better of for worse.
The same limitation emerges in the face of an aristocracy, who have no other interest but to rule on behalf of their limited, elite interests. The minds of the few, no matter how brilliant, cannot foresee the best allocation of resources of the best interests of the people whom they govern, even if they are so morally inclined as to wish exclusively what is in the best moral interest of those whom they lead.
Yet democratic governments transform into fearful monstrosities of mob rule, where majority rule unchecked is in full inhibited sway.
Unicameral leadership of any class was therefore unacceptable.
Divided government representing these clashing interests, in Madison's most enlightened view, was the best way to create a national government that would ultimately govern in the best interests of everyone.
A frustrated and frustrating system by design, the United States Government would ultimately govern best by governing as little as possible.
Dysfunctional and functional at the same time!