But gay marriage is a public matter involving the state, as are civil unions, with attendant property rights. A divided House on this matter cannot stand, for long. That is a whole different kettle of fish. Once civil unions get a bit of seasoning, and become fairly common, SCOTUS will indeed weigh in, if Congress does not. It will really have no choice. Under old tools, it would do so on the grounds of the fundamental right to travel, most likely, although the full faith and credit clause is another available tool.