I’ve therefore been proud to file federalism‐​based briefs on the Cato Institute’s behalf on issues ranging from the civil commitment of sex offenders to Obamacare’s individual mandate to the Voting Rights Act. I yield to no one in fighting to keep the federal government within its constitutional bounds.

And yet all thatfederalism talk is an irrelevant red herring when it comes to gay marriage because there’s no claim here that the federal government is exceeding its lawful authority. Instead, in Hollingsworth v. Perry, the plaintiffs argue that California’s Proposition 8 improperly denies them the fundamental right to marry under the 14th Amendment.

In other words, Perry involves claims that a state government is violating individual constitutional rights, not that the federal government is exercising powers it doesn’t have.

The lawsuit isn’t some novel invention designed to avoid implicating the Constitution’s structural provisions, but the sort of thing that libertarians get behind without controversy in areas ranging from gun rights to property rights to the right to be free from unreasonable search and seizure. And just as there wasn’t federalism problem when the Supreme Court struck down Chicago’s gun ban in McDonald v.Chicago, there would be no federalism problem if it now struck down California’s ban on same‐​sex marriage.

Now, I don’t mean to suggest that Perry is a slam‐​dunkcase that the plaintiffs will easily win. What I’m simply saying is that the case turns on whether treating couples differently on the basis of sexual orientation is constitutionally valid.Perry asks whether theDue Process or Equal Protection Clauses of the Fourteenth Amendment protect the claimed right to marry someone of the same sex. (Full disclosure: Catofiled a brief, which I signed, arguing that the Equal Protection Clause does indeed require states to allow same‐​sex couples to marry—though in my ideal world the government would get out of the marriage‐​licensing business altogether.)

Let me state the background principle: If a state law violates a constitutionally protected right, the federal judiciary has the constitutional authority to strike down that law. Indeed, if federal courts decline to do so—if they engage injudicial “abdication” or “pacifism”—they fail their constitutional duty. Of course, if the state action doesn’t rise to the level of constitutional injury,then courts should rule for the state.

And so if it’s unconstitutional for California to discriminate based on sexual orientation when doling out marriage licenses, then a ruling against Prop 8 would simply vindicate individual constitutional rights. If, however, there’s a compelling reason for making the distinction—because, say, it promotes child‐​rearing— then California can keep doing what it’s doing. Either way, California’s power to regulate marriage isn’t implicated—just like its power over criminal law wasn’t in doubt in 2011 when the Court found the state’s ban on violent video games to violate the First Amendment.

In sum, those who argue that federal courts have no business policing state marriage laws are forgetting that the Civil War Amendments, particularly the 14th, fundamentally changed—perfected—our federalism. Since 1868, when states violate individual rights, they have to answer to federal courts.