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.
Because much of the cooperation between Iran and North Korea is shrouded in mystery, their relationship is ripe for exploitation, particularly by those who are eager to find a hammer to destroy the impending nuclear agreement with Iran. But if this is the only implement that critics can find to inflict damage, they're scraping the bottom of their toolbox of destruction.
What the Venezuela sanctions made clear is that President Obama's opening to Cuba represented exactly zero change in Washington's overall strategy toward the region: The intention of expanding commercial and diplomatic relations with Cuba was mainly to pursue a more effective strategy of undermining the Cuban government -- and all the left governments in the region.