The federal government has ALWAYS had to have it's definition of legal marriage for using among it's own employees.
Today the military and federal government accepts homosexual marriage for itself, and as we can see, all states will recognize it, whether they allow the actual ceremony within their borders or not.
Please reference the oldest federal code defining legal marriage for federal employment purposes. Also please explain why the feds established DOMA if the code was already in the books.
Also please explain why such codes don't violate Clause 3 of Article VI, the prohition of religious tests to be a public servant, since such marriages are associated with the Christian faith.