The first is that gay marriage evangelists are ready to take advantage of that clause in the Constitution (the "full faith and credit" clause) that requires individual states to respect legislation and judicial findings of other states in respect of citizens of those states. A couple who are married in the state of Virginia must be treated, when traveling in Wisconsin, as married. The Constitution (Article IV) does say that "Congress may by general laws prescribe the manner in which such acts, records and proceedings shall be proved, and the effect thereof."
That authority of Congress here is presumably evidentiary, not substantive. Certainly that position will be taken by those who will be citing Article IV as requiring every state to acknowledge as a marriage anything so deemed by the judiciary of the state of Vermont. One might rest easy at the prospect of Vermonters proceeding with their own tribal laws, but of course it would not be so. The Reno, Nev., formula would surely happen again. In the '30s, people who wanted to be divorced, even though the laws in the state where they lived wouldn't grant a divorce, traveled to Reno and came back with their full-faith-and-credit divorces.
These stratagems for avoiding the law in the state in which you live are challenged as never before by that juggernaut determined to go all the way with the license given by the Supreme Court's Lawrence decision, illegitimizing de jure anti-gay legislation. The idiomatic compression of the legal argument would read: Since they can have sex, why can't they marry?
Conservatives correctly tend to back off from such amendments. It is correct that amendments have frequently been proposed in the past to advance tactical objectives, among them the protection of the flag against desecration. But the test now should be framed differently. It is: How does a self-governing republic proceed with a judiciary that has taken to writing basic laws?
Privacy advocates are perfectly free to reason that somehow, implicit in the "spirit" of the Constitution, there is something that permits the destruction of fetal life in deference to the private rights of women. But that is on the order of saying that somewhere in the bowels of Christianity there must be some inchoate provision against consigning anybody to hellfire. Such a position might be taken, pleading the infinite exercise of God's love. But it lieth not in any Christian catechism, no more in any constitutional document that abortion is an absolute prerogative of a putative mother.
The necessary amendment need go no further, nor should go any further, than to limit the application of the full-faith-and-credit clause to exclude any requirement to abide by laws or judicial findings authorizing same-sex marriage. If individual states wish to authorize civil unions between members of the same sex, they would be free to do so, but not free to plead immunities particular to their own state as extending to all 50 states.
This is a tough one for President Bush. But we usefully remind ourselves that the vote of the executive is irrelevant in constitutional amendments. The (required) two-thirds vote of the two branches of the legislature are outside the reach of a presidential veto. But, running for re-election, Mr. Bush's leadership in promoting this defense of marriage would figure prominently in the campaign for approval by three-quarters of the state legislatures.