Do i think the Federal Government will ban gay marriage?
No. What would the motivation be? What would be the precedent[s] cited?
Do i think the Federal Government would not mount an active defense of gay marriage if a given state sought to outlaw it?
Maybe. It would depend on the state and precedent[s] used to justify the endeavor.
May i pose a non sequitur query? What was the Women's March on the day after the Trumpnoguration protesting? What legislation, executive actions, or campaign promises were they seeking to highlight and defeat?