judicial review
It allowed the Supreme Court to overrule an unconstitutional law.
Since it is the Supreme Court that decides what is constitutional and what is not, the decisions of the Supreme Court cannot be unconstitutional, however, it is always possible for the Supreme Court to make new decisions which reverse older decisions. So in theory, if the Supreme Court does something wrong, they will be reversed by a later sitting of the same court (but with new judges).
Strike it down
Strike it down
The SC can declare a law constitutional or unconstitutional.
The law is nullified and may not be enforced against anyone, but it is not "repealed" in the sense that a legislature repeals laws it has made earlier.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.
They can appeal to the United States Supreme Court to have the law be declared unconstitutional by the Supreme Court's right to judicial review.
the supreme court can declare laws unconstitutional
Supreme
"What?" indeed! If the Supreme Court rules it unconstitutional, that ends it. The only ones who can overturn that are some future Supreme Court.
Any state or federal law, executive order or treaty that's relevant to a case under review in a court and operates contrary to the Constitution.
Judicial Review