With a provision that it need not be recognized by other states. That is a small federal government solution, and I think it makes a lot of sense. If you don't want gay marriages in your state, you should make that known in state elections. If you do want them, you should make that known too.
Traditional marriage was understood as so vital to our national survival that the original Republicans named it alongside slavery as one of the two purposes of the Republican party.
That understanding then shaped the destiny of a number of new states admitted to the union. They were forced to outlaw polygamy as a condition for statehood, because anything contrary to traditional marriage would be a destructive force to society.
Thank goodness the federal government ended polygamy.
Now it's time to close the Pandora's box of extending marriage or marriage-like status to homosexuals or any other non-traditional group.