So, the nuclear deal with Iran provides that the Iranians will reduce their number of centrifuges from nearly 20,000 to 5,060. It limits uranium enrichment to 3.67% (well short of weapons grade or even medical grade). It requires Iran to ship all but 300 kg of its enriched uranium (almost 98%) out of the country. It requires the Iranians to shut down one of their two enrichment facilities. It requires their reactor that could produce plutonium from spent fuel to be converted into one that cannot and to ship the spent fuel out of the country. And it introduces inspectors to make sure the terms are kept.
And Republicans are denouncing the deal as dangerous because it does not destroy Iranian nuclear capacity altogether. But the Iranians were never going to agree to that. Acknowledging that in the real world, we can't always have everything we want, which is safer, an Iran with 20,000 centrifuges, or one with 5,060? An Iran with two enrichment facilities or an Iran with one? An Iran with 300 kg of fuel-grade enriched uranium, or one with 50 times as much? An Iran with the capacity to refine plutonium from spent nuclear fuel, or an Iran without that capacity? Hint: This is not a trick question. Why would Republicans prefer the former option?
I don't know, obviously. I have made several guesses, so here is another one. It is based on (1) our experience with North Korea, and (2) a joke Truman's Secretary of State, Dean Acheson, made about the Korean War.
Republicans regard our deal with North Korea as a model of what to avoid. The US and North Korea made a deal in which North Korea sealed its reactor and admitted inspectors to the country in exchange for fuel and reactors that could not be used to make nuclear weapons. However, North Korea repeatedly cheated, eventually abandoned the deal, and built nuclear weapons. Conclusion: No deal is better than an imperfect deal. There are some serious flaws in that account. In 1994, Bill Clinton did, indeed, make such a deal with the North Koreans. The North Koreans did, indeed, regularly cheat and see what they could get away with. But so long as the fuel rods were sealed and weapons inspectors in place, the cheats could be stopped before they got near the threshold of building an actual nuclear bomb. It was a tiresome hassle trying to reign in people who were clearly not acting in good faith. It did, nonetheless, keep the North Koreans from building a nuclear bomb as long as the rods were sealed and the inspectors in place. In 2002, President Bush learned that the North Koreans were experimenting with uranium enrichment and called the whole deal off. It was only then that the North Koreans withdrew from the Non-Proliferation Treaty, expelled the inspectors, and unsealed the fuel rods. Bush, distracted by preparing for the war in Iraq, did nothing. He neither went to war nor undertook negotiations. He resolutely focused on invading Iraq and refused to let the little detail of North Korea expelling its inspectors or unsealing its reactor lead him into doing anything whatever. As the cited article comments, "Before the present President Bush, no one thought that just allowing North Korea to get nuclear weapons was an acceptable option." So blaming the deal for North Korea getting nuclear weapons just doesn't cut it.
And now for Acheson's joke that he recounted in his memoirs. He told it during the Korean War when MacArthur was becoming increasingly insubordinate but any attempt to fire him would make Truman look unpatriotic. As a result, Truman tried to reign MacArthur in, with diminishing success, until he wrote a letter to a Congressman clearly intended to pressure Truman into invading China and the Congressman made the letter public. At this point, Truman had no choice but to fire him. Acheson compared it to the case of a man living by a railroad with his wife and daughter. His wife was very worried about protecting the daughter's chastity from those unruly railroad men and always bothering him with her attempts to protect the girl, the girl's rebellion, what she had been up to, the mother's fears, etc. Finally one day he came home to see his wife crying. She announced that the worst had happened, their daughter was pregnant. The father said, "Thank god that's over!"
Fearing the worse for a long time can make it a relief when it finally happens. There is no doubt that trying to hold North Korea to the terms of the agreement was very stressful and involved a lot of worry and fuss and tiresome back and forth. Maybe to a lot of Republicans, when they finally did get nuclear weapons, their reaction was mostly one of, "Thank god that's over!" Maybe they feel the same about Iran.