From CNN at the time
https://www.cnn.com/2015/03/12/politics/iran-nuclear-deal-treaty-obama-administration/index.html
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Secretary of State John Kerry stressed Wednesday that the administration never intended to negotiate a treaty.
"We've been clear from the beginning. We're not negotiating a 'legally binding plan.' We're negotiating a plan that will have in it a capacity for enforcement," he said at a Senate hearing.
Jim Walsh, a specialist on the Iran nuclear program at the Massachusetts Institute of Technology, said the Iran deal, which commits the United States to waive or lift sanctions, does not rise to the level of a formal treaty.
"Treaties traditionally have involved reductions in armaments, nuclear weapons, conventional forces. They require us to take something away that we have already built or established." In this case, the United States would lift sanctions, but would not be changing its military posture.
"We have had all sorts of agreement that were never ratified by Congress," Walsh said.
But David Rivkin, a constitutional and international law expert who worked for President George H.W. Bush, said that any international agreement requiring major undertakings on the part of the United States -- such as the proposed Iran deal -- must be sent to the Senate for advice and consent.
"The Constitution is quite clear," he said.
When Vice President Joe Biden was a senator in 2002, he wrote a letter to then-Secretary of State Colin Powell charging that a planned strategic arms reductions deal with Russia constituted a treaty subject to Senate approval since it would require "significant obligations by the United States."
Tim Kaine, a Democratic senator from Virginia who has signed onto a bill calling for the White House to put any deal up for a vote in Congress, said that Obama is within his rights to do what he is doing -- up to a point.
"It is not a treaty. If it were a treaty, there is a clear process. It would require a two-thirds vote in the Senate."
But Kaine told CNN on Wednesday that lawmakers did have a role to play at the point when sanctions mandated by Congress are bargained away to ensure Iran sticks to limits on its nuclear program.
"Congress has got to weigh in at some point," Kaine said.