A SC justice does not administer the law. A SC justice makes new law every day through decisions based on application of legal principles to the facts before the court. Except for the occasional mistake by lower courts, for the most part, every decision is new law because it requires sorting out conflicts between existing legal principles that could not be sorted out by lower courts. Where the law is clear and correctly applied, certification is denied.
But that is NOT their job. It's the job of the legislature to MAKE laws, it's the job of the USSC to make sure laws are constitutional or are applied within constitutional constraints.
How much knowledge of the constitution does it take to say "Where does it say that?" If it's not in there, it falls under the 10th Amendment. The only test is that what the states pass does not conflict with the constitution. PERIOD.