"If the SCOTUS isn't the final arbiter, who is?"The PEOPLE, as the founders intended. If you don't believe it, then ponder why the founders included the 2nd amendment.
The USSC may think they have the final word, but if they continue on their present path, they are going to get a rude awakening.
The founders intended for the people to hold a plebescite every time a Constitutional question arose?
Or did they want a civil war whenever people disagreed on whether a search and seizure was reasonable?