The idea that government is not above the law is an example of the principle of limited government. The constitution established checks and balances through the three branches of the government (judicial, legislative, executive) in order to limit the government's power.
The principle of federalism divides powers between state and national governments. That is why the US government is called a federal government. The national government has supreme authority, however it gives autonomy to the state governments through: concurrent powers and reserved powers.
Coining money is an example of a national power. Only the federal government has authority in that matter, the state governments don't have any power over this issue.
The concept that government's powers come from the people is called popular sovereignty. This concept is explicitly shown when people vote for public officers that will be in charge of running the country.