The check on SCOTUS is that it doesn't have any law enforcing powers. They're just men and women in long cloaks writing things down. Also, SCOTUS members can be

The check on SCOTUS is that it doesn't have any law enforcing powers. They're just men and women in long cloaks writing things down. Also, SCOTUS members can be impeached and they can say "no that impeachment is invalid" all they like as the police escort them out of the building. Government is not like programming a computer. If everyone treats the government like it has power, then it has power. If everyone collectively agrees it doesn't have power then it starts to lack power.