The American political system

A perennial concern in the American political system is the potential federal encroachment on state authority. Recent examples of which might be the “Affordable Care Act” or the “No Child Left Behind Act.” What are mechanisms by which states can respond to any such shift in the federal-state balance? How well do they work in maintaining “proper balance.”
Scholars have developed many different models/metaphors/concepts to describe federalism in the United States. Discuss the extent to which these models have moved the subfield forward. Discuss which model you find most persuasive, and discuss whether and why scholars should devote effort to developing models of federalism.