The president’s calls with Mr. Porter have increased in the last few weeks, as the number of people he is close to in the White House has dwindled because of the large number of staff departures, the people familiar with the calls said.

In Mr. Trump’s orbit, few people are ever permanently exiled. He often sees aides who are subject to public criticism as extensions of himself, coming under fire because critics want to attack him, and he has described the Porter situation in those terms to some people, those briefed on the discussions said.

The president has told the advisers he has talked with that he knows he probably cannot bring Mr. Porter back. But he has made clear that he misses the staff structure that Mr. Porter had helped build and implement, a White House official said, speaking on background because advisers were not authorized to discuss the matter publicly. Mr. Porter also served as a de facto deputy chief of staff for policy, playing a key role on issues like tariffs, and Mr. Trump spent as much as two hours a day with him.