Over at opinio juris, Duncan Hollis has an interesting post about whether the agreement reached with Iran on early Sunday morning is legally binding. (I do disagree with Duncan’s title: the “new U.S.-Iran deal” - the deal of course includes other countries). One possible motive for the United States to make this a political, rather than a legal commitment, is to avoid the need for approval by two-thirds of the Senate as necessary for an Article II Treaty, as Duncan notes.
But even if the agreement is legally binding it does not need Senate or even congressional approval, at least as a matter of contemporary and historical practice. It is true that most non-proliferation agreements are concluded as Article II treaties, including the Nuclear Non-Proliferation Treaty. But the Iran agreement lacks some indicia of formality, is short term, does not appear to affect state law, and apparently can be implemented without legislation by Congress. Under State Department practice, all of these factors are relevant to determining the appropriate form of binding international agreements, suggesting that this agreement could be concluded as a sole executive agreement. Moreover, other legally binding agreements of limited scope, designed in some respects to build confidence, have taken this form, including the Hot Line Agreement between the USSR and the US (1963) and the Agreement on the Prevention of Nuclear War (1973). More generally, modi vivendi which “provisionally settl[e] questions whose permanent regulation was left for subsequent treaties” have a long history, as recounted in 1944 by Edwin Borchard here and by Quincy Wright in The Control of American Foreign Relations 239-41 (1922). See also Jean Galbraith’s article here and my article here. The constitutional basis for the President’s power to conclude such agreements might come from the power to receive ambassadors or the power to negotiate treaties. More interesting, perhaps, is whether a similar permanent agreement with Iran and other countries would need to take the form of an Article II treaty, or whether approval by Congress would suffice.
On the question of whether this agreement is binding, it will be interesting to see whether Congress is notified of the agreement pursuant to the Case-Zablocki Act. That Act requires the Secretary of State to “transmit to the Congress the text of any international agreement (including the text of any oral international agreement, which agreement shall be reduced to writing), other than a treaty, to which the United States is a party as soon as practicable after such agreement has entered into force with respect to the United States...” But under the relevant federal regulations, the statute only applies to agreements for which “the parties” “intend their undertaking to be legally binding, and not merely of political or personal effect.”