Last year, Cotton organized a letter from his Republican colleagues in the Senate to Iran's leaders, warning that the next president had the discretion to implement or ignore the nuclear agreement Obama's diplomats were then negotiating.
Shortly thereafter, Iran's foreign minister, Javad Zarif, disclosed that the U.S. and its partners were planning to enshrine the sanctions relief of the agreement in a U.N. Security Council resolution.
(The White House did not send the nuclear deal to the Senate as a treaty, where it would have needed a two-thirds majority for ratification.)
Now there is great uncertainty about what exactly Trump will do when he is sworn into office. Cotton said,
"In January, a President Trump and a Republican Congress will begin a new policy of resolve toward Iran's ayatollahs."
Other Republicans I spoke with on Thursday were not convinced that Trump would tear up the agreement, as many Republican candidates in the primary promised to do.