During that trip, Mr. Mnuchin agreed to a private meeting with China’s top economic official, Liu He, without Mr. Navarro or any other members of the American delegation. He and Mr. Navarro stepped outside to engage in a profanity-laced shouting match, an unmistakable demonstration to the Chinese of their deep differences of opinions. Mr. Mnuchin sought to play down tensions between the American officials, saying on CNBC that Mr. Navarro was “an important part of the team.”