Because things like Corker show us at the end of the day, Cruz WILL "play ball." Therefore, results being "accomplished" is still in doubt.
Obama was going to do the Iran deal without Congress. The Corker bill assured that Congress had the right to approve or disapprove of the deal. The fact that the deal has not received Congressional approval means the next President can nullify the deal.
Trump has said he would not tear up the deal but enforce it. There is no way to make the Iran deal anything but a disaster for the Free World. Cruz said he would shred the deal on Day 1.