The C.I.A. director, John Brennan, in Washington in June. In an interview with the BBC, Mr. Brennan warned that the incoming administration needed to be skeptical about Russian promises.CreditJim Lo Scalzo/European Pressphoto Agency
LONDON — The director of the C.I.A. has issued a stark warning to President-elect Donald J. Trump: Tearing up the Iran nuclear deal would be “the height of folly” and “disastrous.”