In Bond:

It seems to me there — there’s a lot of daylight between the two. Let’s take — and I pick this example not because it’s controversial, but because it relates to an area where the Federal government has never been thought to have authority, namely family law. There are no, you know Federal marriage, Federal divorce, Federal adoption. It’s all been State law. Let’s assume that an international treaty is approved by two-thirds of the Senate and the president which requires States to — to approve same sex marriage. All right? Now, if — if that were a self-executing treaty, same sex marriage would have to be approved by every State. If it is not self-executing, however, it will be up to Congress to produce that result, and Congress would do it or could do it at least by having a Federal marriage law. And then you would have to have a Federal divorce law and, I suppose, a Federal adoption law. I think there is a big difference between just doing it through a self-executing treaty and dragging the Congress into — into areas where it has never been before. I think there is daylight between the treaty and requiring the treaty to be implemented in the fashion that you assert is necessary here.

Verilli seems to suggest that there would be no difference between a self-executing treaty accomplishing this, and a treaty that required implementing legislation.

Scalia says a self-implementing treaty would be feasibly, as the Congress would have to pass additional legislation:

JUSTICE SCALIA: I don’t think it has to be the case. I think there — there’s a great difference between requiring the states by a self-executing treaty to permit same sex marriage and dragging the Federal government or allowing the Federal government to enter into this whole field of marriage, divorce, adoption, family law, where the Federal government has never been.