The Supreme Court decides which cases it wants to hear and there are many cases brought into the legal system each year. That practically gives it the power to make (well, re/interpret) or strike down whatever legislation it wants, as long as there's a relevant-enough case.
Right, but they ideally choose because they think a law needs to be struck down, clarified, etc. based on legal merit and not because of how they or the population feel about the end result.
