There seems to be a it of a divergence between the majority’s conception of Federalism, and that of Justice Kennedy. When Kennedy concurs, all are heeded to draw near.

Justice Kennedy has a refined view of the 10th Amendment, perhaps a relic of the federalism heyday of the Rehnquist Court.

A separate concern stems from the Court’s explanationof the Tenth Amendment. Ante, at 16. I had thought it abasic principle that the powers reserved to the Statesconsist of the whole, undefined residuum of power remain-ing after taking account of powers granted to the National Government. The Constitution delegates limited powersto the National Government and then reserves the re-mainder for the States (or the people), not the other way around, as the Court’s analysis suggests. And the powersreserved to the States are so broad that they remain unde-fined. Residual power, sometimes referred to (perhaps imperfectly) as the police power, belongs to the States and the States alone.

It is correct in one sense to say that if the National Government has the power to act under the Necessary andProper Clause then that power is not one reserved to theStates. But the precepts of federalism embodied in the Constitution inform which powers are properly exercised by the National Government in the first place. See Lopez, 514 U. S., at 580–581 (KENNEDY, J., concurring); see also McCulloch, supra, at 421 (powers “consist[ent] with the letter and spirit of the constitution, are constitutional”). It is of fundamental importance to consider whether essen-tial attributes of state sovereignty are compromised by the assertion of federal power under the Necessary and Proper Clause; if so, that is a factor suggesting that the power isnot one properly within the reach of federal power.

The opinion of the Court should not be interpreted tohold that the only, or even the principal, constraints onthe exercise of congressional power are the Constitution’sexpress prohibitions. The Court’s discussion of the Tenth Amendment invites the inference that restrictions flowingfrom the federal system are of no import when definingthe limits of the National Government’s power, as it pro-ceeds by first asking whether the power is within theNational Government’s reach, and if so it discards federal-ism concerns entirely.

These remarks explain why the Court ignores importantlimitations stemming from federalism principles. Those principles are essential to an understanding of the func-tion and province of the States in our constitutional structure.

Justice Kennedy also remarks on the intersection of federal powers  state sovereignty.

It is of fundamental importance to consider whether essen-tial attributes of state sovereignty are compromised by the assertion of federal power under the Necessary and Proper Clause; if so, that is a factor suggesting that the power isnot one properly within the reach of federal power.