President Trump reportedly has decided on whether or not to certify the multilateral nuclear accord (Joint Comprehensive Plan of Action, or JCPOA) but he won’t as of yet reveal his decision. See this CNN report. For background see this CRS report, Iran Nuclear Agreement (April 21, 2017 R43333). From the report:
The Obama Administration and other P5+1 leaders asserted that the JCPOA represented the most effective means to ensure that Iran cannot obtain a nuclear weapon and that all U.S. options to prevent Iran from developing a nuclear weapon remain available even after the key nuclear restrictions of the JCPOA expire. The JCPOA contains provisions for U.N. sanctions to be reimposed if Iran violates its commitments. Critics of the agreement expressed concerns that the extensive sanctions relief provided under the accord gives Iran additional resources to extend its influence in the region. Critics also assert that the JCPOA did not contain any restrictions on Iran’s development of ballistic missiles. Resolution 2231 prohibits arms transfers to or from Iran, but only for five years, and contains a voluntary restriction on Iran’s development of nuclear-capable ballistic missiles for only up to eight years. The expiration of these restrictions sets the stage for Iran to emerge as a key regional actor. These commitments are stated in U.N. Security Council Resolution 2231. The JCPOA Other critics have said that the JCPOA did not require that Iran cease support for groups that conduct acts of international terrorism.
The Trump Administration has articulated that the United States will seek to counter Iran’s “malign” activities in the region and any other activities that the Administration considers provocative or destabilizing, such as the continued development of ballistic missiles. The Administration has said it is undertaking a “deliberative process” to determine responses to such Iranian activities that would not conflict with implementing U.S. commitments under the JCPOA.
See also, Iran Sanctions (September 15, 2017 RS20871). From the introduction:
The multilateral nuclear accord (Joint Comprehensive Plan of Action, or JCPOA) provides Iran broad relief from U.S., U.N., and multilateral sanctions on Iran’s civilian economic sectors. On January 16, 2016, upon the International Atomic Energy Agency (IAEA) certification that Iran had complied with the stipulated nuclear dismantlement commitments, U.S. Administration waivers of relevant sanctions laws took effect, relevant executive orders (E.O.s) were revoked, and corresponding U.N. and EU sanctions were lifted (“Implementation Day”).
Remaining in place have been those secondary sanctions (sanctions on foreign firms) that have been imposed because of Iran’s support for terrorism, its human rights abuses, its interference in specified countries in the region, and its missile and advanced conventional weapons programs, as well as sanctions on the Islamic Revolutionary Guard Corps (IRGC) and designated commanders, subunits, and affiliates.