FYI Totemo; President can't do that for two reasons; the 10th and 14th amendments to the constitution. THe 10th being States Rights, and the 14, being that what is a legal marriage in one state, is legal in all 50 states.
Personally I would prefer government to get out of the marriage business. Let Elvis minister the marriages! Is the 24 hour church of Elvis still closed?
How about fire all the bureaucrats, and just write checks for every man woman and child, for say the poverty level, that would save taxpayers billions of dollars.
I'd also like to have sheep mowing the white house lawn again, just like in old times.