The JCPOA was a mere executive agreement, not a ratified treaty that becomes the law of the land under the constitution. All the signatories knew what they were getting into when they pursued that route under intense scrutiny from the Senate and the American people. 

Only by a magic trick, known as the Corker Bill, was the Senate appeased, but even that measure required the disclosure to the public of all the side deals--which sadly have never been made public. 

For all the talk of the supposed verification mechanisms, the JCPOA actually hinders inspection. Before ever inspecting a site, the IAEA is required first to ask Iran to explain the nature of that site. Next, the JCPOA provides that Iran must be notified before any inspection of a site occurs. Further, Iran then has the right to further delay an inspection by up to 54 days.

Finally, the JCPOA does not prevent Iran from starting a parallel, separate enrichment program. 

It is actually a roadmap for Iran to build a bomb.