Opponents of the Iran deal have been unable to produce a viable alternative. That is because there really are no alternatives left. Should the Iran deal collapse under the weight of spoilers like Schumer, Iran will get a nuclear weapon. And once Iran achieves and announces that capability to the world, no expert will be able to foresee the consequences.
There are four basic ways people can deal with conflict at different times - competition, avoidance, accommodation and collaborative problem-solving. These strategies depend on the level of concern people in dispute have for their own outcome vis-à-vis the other party's outcome. (It's called the Dual Concern Model.)