Let me start by restating Dr Alf’s, namely:
What is not clear is how US decertification will be received by other parties to the agreement, namely Britain, France, Germany, Russia, China and the United Nations. Of course, there is also the reaction from Iran.
The answer depends on the toughness of the sanctions, how effective they are and whether Russia, China and others are successful in circumventing them. Then, of course, there is the possibility that Israel will want the sanctions toughened against the wishes of Russia and China. Donald Trump may, in the time that it takes to apply sanctions, find himself out of office which then means we are probably looking at President Pence and what he will do with Iran, given America’s need to keep selling arms to Saudi Arabia and keep Israel happy. If the sanctions are effective and damage the Iranian economy, Russia and China will see the precedent being set and will use their leverage which in China’s case is considerable, both in terms of controlling mineral wealth in Africa and their ownership of American debt.
In the end, Russia will be fundamental to reigning in Iran in Syria and Iraq and to helping prevent the rise of a new Ottoman Empire, so I predict an uneasy stalemate. ISIS is now in Afghanistan and operates globally, representing an even bigger long term threat than does Iran. Russia will be needed to contain this threat on their Southern border, China will do so on its borders and in those provinces where Uighurs live and the spirit of jihadism is being fanned by President Erdogan.
The situation is very complex and could easily lead to World War III, which is what the Neocons want, reasoning that they can escape to underground cities already built all across America and ultimately to Mars in future years.
One hopes that sanity prevails.
Dr Alf's Blog 
John, as usual many thanks for sharing your views. I’d like to make an observation and ask a question please.
My understanding is that if Iran violates any aspects of the agreement then the sanctions will automatically be reapplied. So the debate will perhaps not be about the scope of sanctions but more likely about the evidence to support the vioation.
With regard to the US Neocons, is there any evidence of them ‘reasoning that they can escape to underground cities already built all across America and ultimately to Mars in future years’?