Trump says he bombed Iran

[bastion]

A couple of things here:

1) Uranium enrichment does not proceed at a constant, linear rate.  It proceeds at a more-or-less geometric rate.  For example, natural uranium as you dig it out of the ground consists of 0.7% U235 (the fissionable isotope).  To double the enrichment to 1.4% will take a given amount of time that depends on how good your enrichment technology is (gas diffusion, centrifugation, etc.) To double that again to 2.8% will take about the same amount of time, everything else being equal, and so on.  That means that to go from 30% enrichment to 60% takes about the same amount of time as to go from 0.7% to 1.4%.  The other factor is that as you increase the level of enrichment you also have to handle less total material in order to get to weapons grade.  That means that either you need fewer centrifuges or you can use the ones you have with greater throughput.  In other words, the enrichment process goes very slowly at first and then speeds up very rapidly.  When uranium is enriched to 20%, you've done about 90% of the work to take it to weapons grade.  From that point on, it may take only a few weeks to continue enriching it to weapons grade.  

When Obama negotiated the JCPOA in 2015, Iran had a stockpile of 20% enriched uranium.  The 20% enrichment level is the highest level of enrichment for which there are legitimate research and medical uses.  The JCPOA agreement required Iran to get rid of 98% of their enriched uranium by shipping it out of the country, which they did and it was verified by the International Atomic Energy Agency.  That left only a small amount in the country which was legitimate for research and medical purposes, but not enough to enrich into a weapon.  In other words, Iran went from 90% of the way to weapons material to effectively zero percent overnight, as a result of the JCPOA.  That's what Obama paid Iran the $1.7 Billion for.

2) Uranium is typically enriched by first reacting it with Fluorine gas to produce Uranium Hexaflouride (UF6), then heating that compound until it goes from solid to gas phase, and then running the UF6 gas  through the centrifuges.  Once the UF6 gets to the desired level of enrichment for weapons grade, the fluorine has to be driven off to yield metallic uranium.  That requires a multi-step process which requires transporting the UF6 to what amounts to a specialized metal foundry, reducing it back to metallic form, and then carefully machining the metal into the correct shapes for a bomb.  All while making sure than not enough of the metal accumulates in any one spot capable of causing a criticality accident.  When the intelligence agencies say that Iran was not trying to make nuclear weapons, they mean that they had not detected any efforts to transport the UF6 to their facilities where they could turn the UF6 into metal. 

There's no question that Iran has both the knowledge and facilities to produce nuclear bomb cores.  They just haven't made that dash to convert the UF6 to uranium metal.

Agreed with all that - while it does theoretically take only a few months to enrich the 60% iran had to 90% - getting it to weapons grade standard is quite a lot different due to the criticality/localised hotspots and denaturing you mention. Producing a viable format and being able to produce a nuclear weapon would still take them several years even if they still had access to the 60% in the underground reactor US-Israel throtoughly burried last year.

Personally I highly doubt their material science capabilities and ability to relaibly make the perfect spheres required for a proper fissile core - a dirty bomb or very poor yield device would be achievable but they're thankfully a long way off being able to produce fissile cores due to embargoes and impoprt restrictions - the regime have had the nuclear science capacity since the US taught them and Iraq in the 60s to mid 80s under 'Atoms for Peace' and playing iran and iraq against each other but the conversion/transportation to nuke without accidental detination is still a long way off.

Hopefully a new agreement can bring them back down to 5% or below as they were one of only two nuclear plants in the world producing nuclear science/MRI imaging tracing material vital for a lot of modern medicine - Iran only broke IAEA limits after US withdrew from the agreement with no evidence or suppoort from allies. 60% enrinchment was certainly a bit of an FU and blackmail from the regime as it clearly had no civillian use and required quite a lot of technical expertise/redesigning centrifuges from scratch after FLAME/stuxnet wiped the capability out in 2010.

EDIT: There are legitimate radiopahrmiological medicine uses of up to 20% as you state and one of the Iranian reactors was and was a vital supplier of medical isotopes prior to sites being bombed but alternatives are being developed (my cousin is doing her PhD in finding alternatives as most patients experience severe balance difficulties/falls caused by current imaging isotopes).