As with most issues vital to the preservation and health of civil society, the basic responsibility for preserving and strengthening the family should reside at the level of government closest to the people. In their wisdom, the Founding Fathers reserved for the States the authority and responsibility to protect and strengthen the vital institutions of our civil society. They did so to ensure that the voices of America's families could not be ignored by an indifferent national government or suffocated through filibusters and clever legislative maneuvering in Congress.
From doing a quick search of other candidates, even among Democrats, whom I assume (perhaps mistakenly) would be more open to gay marriage, the one consistent thread among all of them is the suggestion that individual states should decide. Usually it is some sort of belief statement on what their opinion is, and then a statement saying that the states should decide it.
I am not wholly against deferring decisions to the states. In my understanding (limited by a political science minor and a catching interest), perhaps more decisions should be left to the states than are left to them already. Two questions then:
1. Does the issue of gay rights and equality, including the right to marry, pertain to the constitution to a degree that requires a national response?
2. When faced with a difficult and divisive question, do candidates defer to federalism in order to duck accountability for their own beliefs?