Actually, it isn't.
"All laws which are repugnant to the Constitution are null and void."
arbury vs. Madison. Source: 5 US (2 Cranch) 137, 174, 176 (1803).
The constitution is either a superior, paramount law, unchangeable by ordinary means, or it is on a level with ordinary legislative acts, and, like other acts, is alterable when the legislature shall please to alter it.
If the former part of the alternative be true, then a legislative act contrary to the constitution is not law: if the latter part be true, then written constitutions are absurd attempts, on the part of the people, to limit a power in its own nature illimitable.
Marbury vs. Madison. Source: 5 US (2 Cranch) 137, 174, 176 (1803).