The Full Faith and Credit Clause makes the Massachusetts gay marriage decision a federal constitutional issue — or will at some point when some federal judge rules that some other state must recognize gay marriages performed in Massachusetts. This is not a federalism issue. The issue is whether one state’s supreme court can impose a policy on the rest of the states. The amendment process is perfectly legitimate, and extremely difficult, as it should be (of course, the courts amend the Constitution everyday, but that’s a subject for another time). This is exactly the kind of conflict — which upsets the balance of power between the states — that merits federal constitutional consideration. An amendment might define marriage, but it might also limit the reach of the Full Faith and Credit Clause. But it is a perfectly legitimate use of the Constitution’s amendment mechanism.