Most Americans oppose same-sex marriage. Almost all Republican politicians say they oppose it, and very few Democratic politicians say they support it. But the opponents are divided in a way that could cause them to lose.

Part of the problem is that some of the opponents are merely professed opponents, not real ones. These are politicians, typically Democrats, who know that the public opposes same-sex marriage but that most liberals favor it. They may, secretly, agree with these liberals themselves. Their strategy has three components: Let the courts impose same-sex marriage on the populace. Claim to be opposed to it. But also oppose any action that would stop the courts from imposing it.

This faction is aided by another: sincere opponents of same-sex marriage who object to a constitutional amendment to ban it. These people believe that states should be free to set their own marriage policies, or that no amendment is necessary, or that the Constitution should not concern itself with marriage policy. People who hold these views should reconsider them, because they may be making a terrible mistake.

Voters in many states have passed referenda to prohibit same-sex marriage, often adding that prohibition to their state constitutions. (Nineteen states have constitutional amendments against same-sex marriage, and an additional 26 have statutes.) But their votes may not ultimately prove decisive. A state court has already imposed same-sex marriage on Massachusetts, and several other states’ courts are poised to do the same thing. Federal litigation designed to accomplish the same objective is underway. Assembling the supermajorities necessary to undo such anti-democratic actions may prove impossible once the deeds are done. (It is no accident that liberal litigators began the campaign for same-sex marriage in two states, Vermont and Massachusetts, where it is relatively hard for voters to amend the constitution.)

States should perform those functions that they can perform. But no state is capable of resisting the federal judiciary if it imposes same-sex marriage. Only an amendment to the U.S. Constitution can protect states from having same-sex marriage foisted upon them by courts.

When the Constitution is amended the old-fashioned way–through the procedures outlined in its fifth article, with a two-thirds vote in each chamber of Congress followed by ratification by three quarters of the states–it almost always reflects a national consensus. An amendment is not an action unilaterally undertaken by the federal government and forced on the states; the states participate in the process. So the federalist objection to a marriage amendment is doubly misguided. Individual states cannot accomplish the good that the amendment seeks, and as a practical matter are unlikely to be oppressed by it.

The leading criticism of the Federal Marriage Amendment is not, however, that it is inconsistent with states’ rights. It is that it would “write discrimination into the Constitution.” We have not addressed that objection because the people we have in mind already know that marriage, and its requirement of sexual complementarity, are not discriminatory. But it is nonetheless worth keeping in mind that this claim of discrimination is being made, and that many people, especially in the legal academy, believe it. If the Federal Marriage Amendment is discriminatory, it can only be because traditional marriage laws are discriminatory–and if that is the case, then it should not take much more argument to get the federal courts to step in. The premises for the federal courts to impose same-sex marriage are being put in place.

The Federal Marriage Amendment is necessary to ward off this danger. We hope it passes in time.