From the Document: "U.N. Security Council Resolution 2231 (2015), which the council adopted on July 20, 2015, implements the Joint Comprehensive Plan of Action (JCPOA) and contains other provisions concerning Iran's nuclear program, Tehran's development of missiles, and arms transfers to and from Iran. The United States has threatened to invoke the resolution's 'snapback' mechanism, which requires the Security Council to reimpose U.N. sanctions lifted pursuant to Resolution 2231 and the JCPOA. The JCPOA, finalized in July 2015 by Iran and China, France, Germany, Russia, the United Kingdom, and the United States (collectively known as the P5+1), requires Iran to implement constraints on its uranium enrichment and heavy water nuclear reactor programs, as well as allow the International Atomic Energy Agency (IAEA) to monitor Tehran's compliance with the agreement. [...] In May 2018, President Donald Trump issued a memorandum stating that the United States would no longer participate in the JCPOA and would reimpose sanctions that had been suspended pursuant to the agreement. Arguing that subsequent efforts by the remaining JCPOA participants, known as the 'P4+1,' were inadequate to sustain the agreement's benefits for Iran, the government has undertaken some nuclear activities that exceed JCPOAmandated limits. Iranian officials continue to assert that Tehran will resume implementing all of its JCPOA commitments if the P4+1 does so."
CRS In Focus, IF11583
Congressional Research Service: https://crsreports.congress.gov/