Withdrawal from International Agreements: Legal Framework, the Paris Agreement, and the Iran Nuclear Agreement [May 4, 2018] [open pdf - 1MB]
"This report outlines the legal framework for withdrawal from international agreements under domestic and international law, and it applies that framework to two pacts that may be of significance to the 115th Congress: the Paris Agreement on climate change and the Joint Comprehensive Plan of Action (JCPOA) related to Iran's nuclear program. [..] Historical practice suggests that, because the Obama Administration considered the Paris Agreement to be an executive agreement that did not require the Senate's advice and consent, the President potentially may claim authority to withdraw without seeking approval from the legislative branch. By its terms, however, the Paris Agreement does not allow parties to complete the withdrawal process until November 2020, and Trump Administration officials have stated that the Administration intends to follow the multiyear withdrawal procedure. [..] As a matter of domestic law, the President and Congress have authority to reassert sanctions lifted pursuant to U.S. pledges made in the JCPOA if they deem the reinstitution of such sanctions to be appropriate, even if such action resulted in a violation of international law. Several possible domestic legal avenues exist to re-impose sanctions, some of which would involve joint action by the President and the legislative branch,and others that would involve decisions made by the President alone."
CRS Report for Congress, R44761