In fact, PC interpretations of the Supremacy Clause (6.2) aside, the Supreme Court has clarified in broad terms that powers not delegated to the feds expressly via the Constitution, the specific power to regulate marriage in this case, are prohibited to the feds.
”From the accepted doctrine that the United States is a government of delegated powers, it follows that those not expressly granted, or reasonably to be implied from such as are conferred, are reserved to the states, or to the people. To forestall any suggestion to the contrary, the Tenth Amendment was adopted. The same proposition, otherwise stated, is that powers not granted are prohibited [emphasis added].” —United States v. Butler, 1936.But we’re not hearing anybody in corrupt DC mention 10A because, despite RINOs now controlling Congress, it is still one of the best-kept secrets in DC.
I think the reason we're not hearing a 10A argument here is because parties who have challenged state marriage laws have skirted the 10A issue. No one (on either side) disputes that the states (and not the feds) have the power to regulate marriage. But, at the same time, no one (on either side) disputes that the states may not regulate marriage (or anything else, for that matter) in a manner which deprives its citizens of the equal protection of the laws.
So, the cases that are challenging marriage laws are not about whether the states or feds have the power to regulate marriage, but rather whether prohibiting "same-sex marriage" deprives certain citizens of equal protection.