He is intensely proud of his accomplishments in the private sector and has repeatedly suggested his tenure in Washington will hurt, not help, his brand and bottom line.

That unfailing self-regard has not endeared him to the rest of the staff. Resentful Trump staff members have long talked about “Jared Island” to describe the special status occupied by Mr. Kushner, who, in their view, is given license to exercise power and take on a vague portfolio — “Middle East peace” and “innovation” are its central components — without suffering the consequences of failure visited by the president on mere hirelings.

Adding to the animus is Mr. Kushner’s aloof demeanor and his propensity for avoiding messy aspects of his job that he would simply rather not do — he has told associates he wants nothing to do with the legislative process, for instance. He also has a habit, they say, of disappearing during crises, such as his absence on a family ski trip when Mr. Trump’s first health care bill was crashing in March.

Mr. Bannon, a onetime Kushner ally turned adversary known for working himself into ill health, has taken to comparing the former real estate executive to “the air,” because he blows in and out of meetings leaving little trace, according to one senior Trump aide. Just as Mr. Trump does, Mr. Kushner quickly forms fixed opinions about people, sometimes based on scant evidence. But Mr. Kushner is quicker to admit when he has misjudged a situation, and to change course.

Despite the perception that he is the one untouchable adviser in the president’s inner circle, Mr. Kushner was not especially close to his father-in-law before the 2016 campaign. The two bonded when Mr. Kushner helped to take over the campaign’s faltering digital operation and to sell a reluctant Rupert Murdoch, the chairman of Fox News’s parent company, on the viability of his father-in-law’s candidacy by showing him videos of Mr. Trump’s rally during a lunch at Fox headquarters in mid-2015.

When asked by friends and associates to describe the source of his influence over the president, Mr. Kushner has offered explanations rooted in loyalty, family and, above all, his acceptance that Mr. Trump is a 70-year-old man of fixed habits who cannot be easily diverted from a course of action.

Mr. Kushner is fond of telling friends that he does not have “any vested interests” beyond seeing his father-in-law succeed. Many of the people working for Mr. Trump are not “looking out for the boss, but I am,” Mr. Kushner told a visitor recently.