Without them, the national government will routinely succumb to interest-group entreaties to wipe out jurisdictional competition. American government lost such constraints some six decades ago, when the constitutional notion of limited and enumerated federal powers collapsed in the wake of the New Deal. The reestablishment of constitutional constraints requires a Supreme Court with the will and the nerve to assert principled, constitutional limits to national power. No other institution, least of all Congress, can be relied on to obey and enforce those limits. But the Supreme Court cannot enforce the constraints on federal power enumerated in the Constitution on its own.
Principled federalism implies the repeal of many federal statutes enacted over the past six decades.
That is out of the question, however. In 1937, when President Roosevelt threatened to pack the Supreme Court with appointees who could be relied on to sustain expansive federal statutes, the Court learned that it could not unilaterally safeguard constitutional norms against dominant political majorities. Federalism, in short, needs a constituency. Were the Supreme Court to endorse, embolden, and legitimize those constituencies, they would in turn defend the Supreme Court and its federalist jurisprudence against political assaults. The difficulty with envisioning that success lies in the particulars, not in the general analysis.