“It will not be denied that power is of an encroaching nature and that it ought to be effectually restrained from passing the limits assigned to it. After discriminating, therefore, in theory, the several classes of power, as they may in their nature be legislative, executive, or judiciary, the next and most difficult task is to provide some practical security for each, against the invasion of the others.” — James Madison, 1788, Federalist No. 48
The brilliance of the Constitution, and the secret to its enduring strength, is not that the Founding Fathers assumed that there would always been men of goodwill and unimpeachable integrity to administer government, but that they understood unequivocally that it is the nature of nearly all men in power to attempt to expand that power. In writing the Constitution, the Founders engaged in a sort of moral physics, pitting the force of will of one branch of power, or one level of government, against the others, so that no one branch could become despotic and tyrannical.
In doing so, they separated government into two levels, the federal and the state, with the federal government granted primacy over the states when exercising one of a limited and defined set of “enumerated” powers, and all other powers being retained by the states, or the people directly. They also divided government into three branches; the executive, the legislative, and the judiciary, with the legislative, being most directly accountable to the people, retaining the most power, but with each branch provided checks and balances to limit the expansion of power by the other branches.
Their foresight proved prophetic, as for more than two hundred years government power has been in a tug-of-war between the state and federal governments, and the three branches of government.