Constitution of the United States was written in 1787, ratified in 1788, and has been in operation since 1789. It is the world’s longest surviving written charter of government.  

        Hence we say, that the Constitution of the United States is a glorious standard; it is founded in the wisdom of God. It is a heavenly banner; it is to all those who are privileged with the sweets of liberty, like the cooling shades and refreshing waters of a great rock in a thirsty and weary land. It is like a great tree under whose branches men from every clime can be shielded from the burning rays of the sun.                   --The Mormon prophet Joseph Smith . .
Its first three words - “We The People” -  affirm that the government of the United States derives its power from its citizens.  The supremacy of the people is first stated in the Declaration of Independence, upon whose authority the Constitution rests.

We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.  That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed,

The people exercise their power through their elected representatives as establioshed in Article I, which creates a Congress consisting of a Senate( which represented the states) and a House of Representatives. (which represents the people). The positioning of Congress at the beginning of the Constitution reaffirms its status as the “First Branch” of the federal government.

The Constitution assigned to Congress (he states and the people acting together) responsibility for organizing the executive and judicial branches, raising revenue, declaring war, and making all laws necessary for executing these powers.  The president is permitted to veto specific legislative acts, but Congress has the authority to override presidential vetoes by two-thirds majorities of both houses.  The Constitution also provides that the Senate advise and consent on key executive and judicial appointments and on the ratification of treaties.

For over two centuries the Constitution has remained in force because its framers successfully separated and balanced governmental powers to safeguard the interests of majority rule and minority rights, of liberty and equality, and of the central and state governments.  A document which specifically limited the powers of the federal government, its balancing powers were eroded by unwise amendments - 12th Amendment in 1804, and th 16th and 17th Amendments in 1913. Like the Jewish Torah, the Constitution has been interpreted to meet the changing needs of a modern society profoundly different from the eighteenth-century world in which its creators lived. The interpretations can be reversed, but we are pretty much stuck with the amendments.