It is a treaty, by any rational traditional definition. There was a good reason to mandate treaty approvals when the constitution was drafted. The same reason applies. This is not just political fun and games over who can get rich making blood money deals with Iran. Iran has been financing the militants in Irag, Afghanistan, even factions in Syria, and of course Hizbollah and In Yemen as well. Yemen being a great example of how naiive the administration is, touting their lame drone kills as big wins while the pro-Saudi and pro-US government literally collapsed and we had to evacuate our embassy under cover of darkness much like the proverbial rats and the sinking ship. Same guys think the Iran deal is pretty much OK.