"The Obama Administration and other P5+1 leaders asserted that the JCPOA [Joint Comprehensive Plan of Action] 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. [...] 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. [...] In the 114th Congress, some legislation was introduced with the stated purpose of redressing asserted weaknesses of the deal or preventing any U.S. sanctions relief beyond that explicitly promised in the JCPOA. Some of that legislation, as well as new proposal, has been reintroduced in the 115th Congress."
CRS Report for Congress, R43333
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html