It's called State Sovereignty...AKA the 10th Amendment. Too bad our government has been conveniently ignoring this for over 100 years.
Technically though....Federal law does override State law. BUT the constitution grants each individual state sovereignty.
The 10th Amendment protects the laws that a certain state wants to make....unless it's already a law in the constitution.
nothing could be farther from the truth.
the constitution makes it clear that the federal government's role is to "regulate" (that is, make regular, ensure the continuance, fairness and freedom of) trade between the states, represent the states as a united front to foreign powers, secure our international sovereignty and borders, and prevent one state or the federal government from interfering with affairs of another state.
for these jobs, the federal government was chartered with certain authority, and powers granted to it BY THE STATES, and granted to the states BY THE PEOPLE. the federal government was created by the states, who draw their authority from the people, not the other way around. within the state,, the state's constitution, or charter is supreme, only when another state or a foreign land is involved does the federal government have any power or authority.
over the last 200 years, the people have lost their power to the state's and the fed's encroachment and power grabs, and the states have been turned into subservient dogs by their new masters in washington. This is the result that the founders warned against, and it has come to fruition.
both of the major political parties had a hand in it, both supported it, and both profit from it.
our constitution is now nothing more than a crusty old paper in a glass case. it has no meaning no power and the people are slaves to the mandarins who run washington. nice job electorate. nice job.