he led the lengthy negotiations that produced the iran nuclear code, the administration's signature foreign policy achievement. trump, during his presidential campaign, called the deal insane and a disaster. on may 7, 2018, trump tweeted about mr. kerry's, quote, possibly illegal shadow diplomacy, an apparent reference to mr. kerry having conversations as a private citizen with iranian and other officials. trump tweeted another attack on mr. kerry the next day, the same day trump announced the united states was withdrawing from the accord. an justice department officials told his office he would be responsible for investigating mr. kerry's iran-related conduct. the fbi would join the inquiry. the focus was on the logan act, a rarely evoked 1799 statute barring private citizens from unauthorized negotiations with foreign governments, which has been criticized as unconstitutionally vague. mr. berman notes no one has ever been successfully prosecuted under the law, but the conduct that had annoyed the president