Secondly, the Constitution is the Supreme law of the land. Finally, the justices took an oath to uphold the Constitution, and they could not stand to see it violated. Also, the Supreme Court has adapted the power of incorporation. They incorporate national law against the states, in essence making their own law. They can do this because they are the final and ultimate interpreters of the Constitution.
Incorporation usually happens with the Bill of Rights and the Fourteenth Amendment.
The Fourteenth Amendment is a Bill of Rights against the states, but it only guarantees liberty. The Supreme Court has defined liberty as the rights guaranteed in the Bill of Rights and incorporated them against the states. The Court is perhaps its own greatest inhibitor, which is why I think we can easily avoid a judicial oligarchy. First, the court retains the right to review itself and to overturn its own decisions. This has happened over 130 times in our history.