"If tariffs are such a good economic idea, then why stop at national boundaries? If they make everyone richer, why not have customs posts between New York and New Jersey? Cars entering and leaving the Lincoln tunnel would have to pay, on top of the toll, a surcharge on all the goods they contain. Why not, indeed, make New York and New Jersey self-sufficient in all their needs, making all their own cars, growing all their own food etc?"

From the Economist.