For weeks, Mattis had been resisting requests from the White House to provide military options for Iran. Now Trump made clear that he wanted the Pentagon to deliver a range of plans that included striking Iranian ballistic missile factories or hitting Iranian speedboats that routinely harassed U.S. Navy vessels.

“Why can’t we sink them?” Trump would sometimes ask about the boats.

National security adviser H.R. McMaster and his staff laid out the president’s request for Mattis in a conference call, but the defense secretary refused, according to several U.S. officials, who spoke on the condition of anonymity to discuss sensitive internal deliberations. At that point, McMaster took Mattis off speakerphone, cleared his staff from the room and continued the conversation.

“It was clear that the call was not going well,” one official said. In the weeks that followed, the options never arrived.