http://thedailybanter.com/2015/03/how-not-to-do-diplomacy/
"While the letter’s signatories are U.S. senators, that does not mean they have the “authority of the United States” as required by the law since when it comes to conducting foreign policy, the executive branch is the United States, taking into consideration the occasional “Advice and Consent of the Senate” as prescribed by the Constitution. However, this letter is neither advice, nor consent. It’s directly addressed to leaders of a foreign government presently involved in talks with the U.S., and it is designed to thwart those talks. Unless the senators were authorized by the president to address Iran’s leaders in this letter, a case can be made that 47 U.S. senators just violated a federal law that carries a prison term of up to three years."
