Under Congress's constitutional Article IV, Section 1 authority which allows Congress to legislatively determine the extent to which one state has to respect the records of another state, the significant DOMA provision which still stands is Section 2 below.
DOMA:
This Act may be cited as the "Defense of Marriage Act".
No State, territory, or possession of the United States, or Indian tribe, shall be required to give effect to any public act, record, or judicial proceeding of any other State, territory, possession, or tribe respecting a relationship between persons of the same sex that is treated as a marriage under the laws of such other State, territory, possession, or tribe, or a right or claim arising from such relationship.
In determining the meaning of any Act of Congress, or of any ruling, regulation, or interpretation of the various administrative bureaus and agencies of the United States, the word 'marriage' means only a legal union between one man and one woman as husband and wife, and the word 'spouse' refers only to a person of the opposite sex who is a husband or a wife.
Note that Section 3 above is what the Supreme Court ruled unconstitutional. And I agree with the Supreme Court because the states have never delegated to Congress, via the Constitution, the specific power to regulate marriage. Only the states can regulate marriage. And only the states can amend the Constitution to define marriage. The problem is that the states, including low-information state lawmakers, have been asleep at the wheel concerning such issues.
Also, probably the main reason that patriots tremble in their boots when activist judges rule in favor of the pro-gay movement is the following imo. Low information-patriots evidently do not understand that the states have never amended the Constitution to expressly protect gay marriage which this judge seems to be ignoring. So the states can actually make laws which distriminate against things like gay marriage, imo, as long as such laws don't also unreasonably abridge constitutionally enumerated rights.
Unlike our present President, I don't claim to be a constitutional scholar. However, the first sentence here is pretty straightforward. Based strictly on it, any state must recognize the marriages that are legal in every other state.
"Congress may by general laws prescribe the manner in which (they) shall be proved" is also pretty clear. It means Congress prescribes the methods by which judicial acts in one state, such as marriages, are to be documented for acceptance by another state.
"Congress may by general laws prescribe ... the effect thereof." is where the interpretation comes in. Given the Founders' notorious suspicion of federal power, I seriously doubt they intended to give Congress the power to exclude certain "public acts, records, and judicial proceedings" from the requirements of the first sentence whenever it so chose. This would give Congress, in essence, the power to decide which "public acts, records, and judicial proceedings" of the states need be accepted by other states. If that was their intent, why didn't they just say so?
I suspect the Defense of Marriage Act is unconstitutional for perfectly conservative and states' rights reasons.
Does Congress have, or should it have, the power to decide which state laws must be respected by other states? Or did the Constitution intend to give Congress the power to regulate how such laws would be communicated between states?