The Iranian nuclear deal (more on the deal and the secret side agreement; see also this) refers to uranium enrichment thresholds of 5% and 20%. These may not sound too threatening, given that a nuclear weapon requires enrichment to around the 90% level. BUT the percentage enrichment of the uranium is NOT a good indicator of the amount of work required to get there.
Start with a tonne (2204 pounds) of natural uranium feed–to enrich it to 5% will require about 900 Separative Work Units–SWUs being an indicator of the amount of energy, time, and capital equipment required for the process. Take to 5% enriched product and continue enriching it to 20%, and the incremental cost will be only about 200 SWUs, for an accumulated total cost of 1100 SWUs. And if you want to turn the 20% enriched substance into weapons-grade 90%-enriched uranium, you need add only about another 200 SWUs of effort, for a grand total of 1300 SWUs. Thus, the effort required to get to that seemingly-harmless 5% threshold is already 69% of the way to weapons grade, and 20% enrichment is 84% of the way there. See this article, which explains that “the curve flattens out so much because the mass of material being enriched progressively diminishes to these amounts, from the original one tonne, so requires less effort relative to what has already been applied to progress a lot further in percentage enrichment.”
There has been very, very little media coverage on this point. One place the issue was discussed was in February and September 2012 reports by the American Enterprise Institute, which were discussed and excerpted at PowerLine in November 2013. Note that the AEI analysis shows an even flatter enrichment curve than the one in the article I linked above–AEI is showing 90% of the total effort for weapons-grade as being required to get to 5% enrichment, rather than “only” 69%. In either case, it should be clear that possession of large quantities of material enriched to 5% is a very nontrivial milestone on the way to constructing a nuclear weapon.
Meanwhile, 4 billion dollars worth of frozen Iranian funds are being unfrozen and sent to Iran. Money is fungible, and almost certainly some of this money will go to support Iranian-backed terrorism, funding operations intended to kill American military personnel, Israeli civilians, and quite possibly American civilians in this country as well. And some of it will probably go to support R&D on advanced centrifuge technology, allowing Iran to move even more quickly to a nuclear weapon when it decides to do so.