As america is getting stuck on the ukraine case they are now trying to make the issue more complicated. After rest of the world Russia China and others completely understood what they are they now cant convince anyone against Iran with whatever excuse. Even the nuclear talks are on the run these sanctions are unexplainable but an item of provacation.
This time it seems they want to go to target directly. They want Iran to react to sanctions and finish the nuclear dialogue transparency etc. this way they will create the excuse for more sanctions and even war.
It is better for Iran to keep the current nuclear policy and do not cut off the nuclear dialogue. Russia is also sanctioned by west and Iran can turn to Russia for trade along with South American countries in food exports for example that Russia put sanctions to eu countries and many other fields. This way non american controlled countries can form a block within themselves and gradually obtain self sufficiency as a trade and security bloc.
Also after getting stuck everywhere Syria Iraq(not totally they should thank to isis) and ukraine they are more dangerous now. since the guys are war criminals as was seen on the ghouta chemical attack case every harm can come from them.
Countries Iran and also Pakistan need to possess second strike capability. There should be sufficient capability of chemical and biological mrbms to be launched from warships in case of Pakistan nuclear mrbms. Also I think submersible ballistic missile erector launcher platforms can be designed which can be lifted up by a submarine(by pumping air etc.) and lock to its place to erect and launch above water in the abscence of submarine underwater launched ballistic missile capability. This way preemptive nuclear strike option will fade away from the criminal minds as well.