The law is nullified and may not be enforced against anyone, but it is not "repealed" in the sense that a legislature repeals laws it has made earlier. The unconstitutional law will remain on the books until the appropriate legislature makes an actual repeal to clear the books of the now useless law.
The Supreme Court of the Unites States may declare laws unconstitutional. It is the only branch legally able to do that.
the supreme court decides
who decides whether or not the supreme court will review a case
who decides whether or not the supreme court will review a case
Supreme
The Supreme Court
The Supreme Court alone decides which cases, and how many they will hear.
The Supreme Court alone decides which cases, and how many they will hear.
The supreme court
judicial review
Supreme Court
Supreme Court