The American political system has been held up as an ideal for division of political labor. This is not the only system based on a constitution, of course, and an analysis of many different societies through history shows me that a system with a constitution is a system in which the people can point to a clear legal basis for their political structure. A constitution is a social covenant in written form, not merely a tacit agreement but an actual document by which subsequent actions can be judged. The American political system has survived and evolved precisely because there is a written document accepted and applied by the people. We may change how we view specific provisions, but we do not have to guess at what those provisions are. The people and the sovereign are both subject to the same regulating document as a framework for institutions and actions alike.
The forms of political institutions should serve the needs of the people they serve and should uphold and promote the values that those people want to elevate to special status.
We hold a number of values to be important enough to be placed in this status — freedom, equal rights, self-government, and so on. It is thus necessary to determine what values are to be protected and promoted before creating the political institutions that will serve that purpose, and a constitution then becomes the document that creates those forms and assures their continuance. This is not an easy process, nor is it a process that takes place and then stops. This is why the flexibility of the American system is so valuable — it provides for change and evolution over time. The basic political structure in that system balances power between three branches of government and between a federal system and a state system. Over time, power has shifted around in this system for different needs and environmental changes. Loomis explains the way this system was.