Technically, this would probably be a Washington State Constitution wins. The Federal Constitution has nothing to do with performing marriages. Only in recognizing documents and contracts issued in other states.
Yes you are right but I was thinking of the 10th Amendment being adhered to.
That is not true. Here is the law... pay attention to the red typeface.
Article IV.Section. 1.
Full Faith and Credit shall be given in each State to the public Acts, Records, and judicial Proceedings of every other State. And the Congress may by general Laws prescribe the Manner in which such Acts, Records and Proceedings shall be proved, and the Effect thereof.
Only Congress can define the effect by law...