President Trump made history over the weekend when he became the first sitting American president to step into North Korea. But the biggest impact of that gesture may have been on Iran. Guest: David E. Sanger, a national security correspondent for The New York Times and the author of “The Perfect Weapon: War, Sabotage, and Fear in the Cyber Age.” For more information on today’s episode, visit nytimes.com/thedaily.  Background reading: Trump administration officials are at odds over what demands to make in new talks with North Korea, with some now considering a nuclear freeze as a first step.Iran on Monday violated a key element of the 2015 nuclear deal, from which Mr. Trump withdrew the United States last year.