Trump cannot disolve the JCPA by unilateral executive order
Trump is taking it on his own to completely destroy the faith in the US to make agreements and treaties. I don't believe that he has the right to decertify Iran's compliance on his own. He has become the worst of the extreme right and the Neocons. He is implementing their agenda in an arbitrary and impulsive way. The JCPA solved a problem. Iran is not developing nuclear weapons, however the DPRK is, and they are watching how agreements with the US work out.
A summary of the Agreement:
Parameters of prospective actions by P5+1
Lift all sanctions within 4 to 12 months of a final accord.
Develop a mechanism to restore old sanctions if Iran fails to comply as per IAEA reports and inspection.
The EU will remove energy and banking sanctions.
The United States will remove sanctions against domestic and foreign companies who do business with Iran.
All UN resolutions sanctioning Iran will be annulled.
All UN-related sanctions will be dismantled.
Parameters of prospective actions by Iran
Reduction in the number of installed centrifuges from 19,000 to 6,104 and only 5,060 of these enriching uranium for 10 years.
Not enrich uranium above 3.67% purity (suitable for civil use and nuclear power generation only).
Reduce stockpile of enriched uranium from current 10,000 to not more than 300 kilograms 3.67 percent enrich uranium for 15 years.
Fordo uranium enrichment facility will operate not more than 1,000 centrifuges for research. 5,000 R-1 centrifuges will be running at Natanz. The remaining 13,000 centrifuges will be used as spare, as needed.
Arak facility will be modified so as to produce a minimal amount of plutonium but will remain a heavy-water reactor.
Allow inspection of all its nuclear facilities and its supply chains such as uranium mining sites .
Trump cannot unilaterally decide that Iran is in breach.
This describes his duties and the status of treaties as made by the US:
2: This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land;
1: The judicial Power shall extend to all Cases, in Law and Equity, arising under this Constitution, the Laws of the United States, and Treaties made, or which shall be made, under their Authority;
One could argue that the JCPA is not a treaty. However it is pretty clear as to the terms of the agreement, that Trump cannot declare Iran in breach of the treaty, only the IAEA has that authority. I believe that the US entered into this agreement under actions of the Executive with the agreement of other countries as parties to this agreement, including a vote in the UNSC, and therefore is the same as a treaty.