It's all about nuclear weapons - that's all. We can talk about sanctions and overthrows or anything else you want, it doesn't matter. Iran has been actively seeking nuclear weapons for 40+ years and at every turn the USA has blocked them. Diplomacy won't help, leaving them alone won't help, a change in US government wont help, nothing will help except allowing Iran to possess nukes - and nobody wants that, not even China and Russia. I'm not saying anything new or provocative, that's the reality - the want a nukes and no amount of appeasement or diplomacy is going to change that.
And, if anyone thinks the "nuclear deal" was working - think again, they were at 20% enrichment when the deal was signed, now they're saying that they're inside of a year from developing nukes. Yeah, they didn't skip a beat - probably ramped it up after securing the $150B.