I think the fed will have an issue enforcing law if nullified. With today's political environment and communication systems, the mass violence necessary to enforce law against state nullification will not play well to the public, and I'm not convinced that modern media can spin it so it does.

In reality, the system is a naked king. It really only holds together based on a gentleman's agreement, and otherwise, pure physical power. No branch or state is really "required" to follow any law in the big scheme. The founders understood this, but they also understood the power of myth, and the constitution and all the theorizing that surrounds it is just that. It's just a myth.