On 9 March 2015, 47 Republican US Senators wrote an open letter to the Islamic Republic of Iran purportedly to explain how the American system of government works in regards to international agreements. It states, in essence, that no agreement will be binding on the United States without ratification of the Senate, or at a minimum, passage by the Congress as a whole to pass it into law. Otherwise, it would be subject to cancellation by any future administration on a whim.
The Senators, to a degree, have a point. In the American constitutional system there is a limit on the President’s ability to make treaties, international agreements, without congressional involvement. As a matter of American law, as separate from International Law, this is true. However, an international agreement, a treaty, is not only a creature of American law, it lives outside itself at the international level as a binding agreement between States – enforceable between States, regardless of its characterization under national law.
Of importance here is that for an agreement to be binding under International Law it need only be negotiated by, inter alia, “Heads of State” and the expressing the intent of the State to be bound by the agreement. From this point forward the agreement is enforceable at the international level. The formal ratification of the agreement by the Senate, unless written into the text of the agreement itself, is not a requisite for the treaty to be enforceable.
It is true that future American administrations could disavow the agreement, and that Congress could act to undermine its execution. This is the same choice any State faces when it wants to break its international obligations, something that does happen with a certain regularity, unfortunately. However, when done by the United States it continues a disturbing precedent that undermines the entire international system by delegitimizing its conflict resolution mechanisms. It also tends to add fuel to the argument that International Law is nothing more than power politics written down on the page. This is not what any peace loving society should desire, and runs counter to the goals that the Senators seem to be advancing.
While the 47 Senators are correct that a non-ratified agreement is not law in the United States, they underestimate the damage that ignoring such a treaty would have for international peace and security, and its value under International Law.
 The Vienna Convention defines a treaty as “means an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation.”
 For the line on this distinction, see the Avena cycle of cases.
 See, Vienna Convention Arts. 7, 11.