[rayiner]

The National Minimum Drinking Age Act didn't "force states" to do anything. It provided that the federal government would withhold 10% of highway funds if states did not enact a drinking age of 21--it had to use a carrot/stick approach precisely because the federal government could not directly compel states to legislate.

That distinction, moreover, is not "theoretical"--it is a limit on federal power that has real teeth. In NFIB v. Sebelius, a majority of the Supreme Court (7-2, on that point) held that ACA's Medicaid expansion was "unconstitutionally coercive" because it would allow the federal government to withdraw all of a state's Medicaid funding if the state did not expand Medicaid eligibility under state law.

Gay marriage, drugs, and immigration are other significant areas where states have used their prerogatives to depart from and refuse to enforce federal law.