The thing is, whether the deal was ratified by Congress or not, all the countries involved were abiding by it, until the US unilaterally violated it by immediately imposing sanctions. Iran was not enriching beyond 3.67% which is adequate for power production. It did test fire ballistic missiles that were designed for conventional warheads. The UN and US frowned upon it, but did not consider it to be a violation. For over 40 years, the US has been working to force regime change and install a puppet government in Iran that will kowtow to US interests, and obviously it's still at it. For most of this time, the US has imposed sanctions on Iran, causing untold deaths and suffering for Iranian civilians. Is it any wonder why Iran hates and distrusts the US, and why its leaders refer to the US as "The Great Satan?"
I have little doubt that Iran actually does want a nuclear weapon, but not for offensive purposes. It knows that would be suicide. Iran knows the US is very much deterred from running regime change operations on nuclear-armed countries. And that's also why the US is so intent to prevent Iran from becoming nuclear-armed. Make no mistake. The US is pulling yet another regime change attempt on Iran, just like it did to Venezuela, Syria, Libya, Ukraine, Iraq, etc. Stop believing the propaganda.