Shell saidBut if Obama "supports" it, and has the power to "change" it, but won't, what's the point of having him in office?
No President has the power to unilaterally make law, nor rule on the Constitutionality of laws. Those powers rest with the Congress and the Supreme Court, respectively.
What a President can do is issue Executive Orders, which have limited application. And in the case of gay marriage, that authority falls to the States under our Federal system. Much the same way you get a driver's license from your State of residence, not from Washington, DC.
Hence DOMA may have exceeded the role of the Federal government, by attempting to regulate marriage on the national level, and to deny marriage recognition granted by individual States.
The Obama Administration has taken the extraordinary pro-gay step of refusing to defend the DOMA law in the courts. Whereas the Republican Party, including Romney, have sworn to defend & enforce the provisions of DOMA, and even more, to outlaw all existing and future gay marriages & civil unions with a Constitutional amendment.
When Obama says gay marriage is a State issue he is Constitutionally correct. And consistent with the arguments his Administration has brought against DOMA, as an unconstitutional act by the Federal government that violates States rights.
As you note, DOMA will need to be undone at the federal level, either by being declared unconstitutional by the Supreme Court or by being repealed by Congress.
When gay marriage is passed at the state level, I believe that it'll need to go through the courts for one state w/o marriage recognition to be forced to recognize a marriage performed in another state. This would be achieved through the "Full Faith and Fealty" clause of the Constitution.
The Executive (Obama) cannot unilaterally undo DOMA. However the President has profound influence on what's done in Congress and what priority they place on legislation. "Obamacare" is a good example. He could have pushed hard for repeal of DOMA. He's not going to do that.
It was disingenuous at best for Obama to state that the matter needs to be resolved at the state level when DOMA still remains at the federal level. My feeling is that he came out for gay marriage long enough to collect fat donations from wealthy gay donors who had been holding back, then flipped just before the election to pander to devout Chrisian blacks.
We've been thrown under the bus, but most of us will still be voting for the guy.