And it's failings....
The Defense of Marriage Act of 1997 was a law enacted by Bill Clinton and the Republican Majority during the 1990s which established the following: For federal purposes, Marriage is only valid for one man and one woman. Further, authorizes states to decide for themselves what constitutes a valid marriage and to define that validity. Here's the problem:
The 10th Amendment does not give the Federal Government the authority to establish guidelines of what constitutes marriage. That is for the states to decide. "Powers not expressly granted to the Federal Government or prohibited to the states are reserved for the states or to the people." 10th Amendment of the US Constitution.
Here's problem number two:
The full faith and credit clause is a section of law in the US Constitution Article IV, Section 1: "Full Faith and Credit shall be given in each State to the public Acts, Records, and judicial Proceedings of every other State. And the Congress may by general Laws prescribe the Manner in which such Acts, Records and Proceedings shall be proved, and the Effect thereof.
The Defense of Marriage act, again oversteps it's bounds by violating constitutional law, placing this act above the stated text of the constitution itself. By giving states the authority to decide which records they deem as vaild, they are essentially saying to states, "Now you can pick and choose what to accept as legal from another state." Our founders wanted to avoid this issue by writing the clause in the first place. They wanted every state in the union to be equal in status to another. Now, here's another similar legal scenario. Abortion in every state is different, regarding time and length of pregnancy. Some states allow it up to the 6th month...and others to the end of the first trimester. If a mother wants an abortion, but her state only allows 3 months, and she's 4 months, then she can go to a neighboring state and get one where it's legal. However, the state she lives in cannot prosecute her for doing so, as they do not have jurisdiction in that state. Same with marriage, if I get married in Massachusettes, and move to South Carolina, then, following past prescident, SC would be legally required to recognize my union, regardless of the state's "religious" objections to my type of union. As we do not live in a theocracy, nor does SC have the legal right to deny me services that are exclusive to marriage, they're just kinda crap out of luck, and they have to deal with it, just like any woman getting an abortion in another state.
Now, this creates a nasty prescident in law, which now gives states a reference to refuse recognition of drivers' licenses as valid ID, or marriage licenses, certificates of death or birth, etc. You cannot pick and choose individual documents to declare as valid for one state and not another. And the Federal government can't either, as it is not their right.
So, basically, The Defense of Marriage act has little legal ground to stand on, and will most likely fall. Any justice trying to use "past prescident" as opposed to constitutional absolutism will ultimately see their credability shot in half as a result.