Executive Discretion and the Iran Deal
A presidential policy (which is what the deal is) is just a policy. It isn't, and constitutionally cannot be, a law.
Does the Iran Deal Bind the Next President?
the argument for congressional authorization is embarrassingly weak, and without congressional authorization any presidential attempt to make a binding deal is almost certainly unconstitutional.
Two Reasons the Iran Deal Is Unconstitutional
In sum, the Iran deal is unconstitutional (a) because the President has not taken sufficient action to assure that it is nonbinding under international law, and (b) even if it is nonbinding under international law, it should be only a commitment of the current President and should not purport to be an undertaking of future Presidents for whom the current President cannot speak.