Mr. Bannon’s reputation is overrated. Yes, he transformed Breitbart from an irreverent blog into the iconoclastic tribune of nation-state populism, the anti-elitist ideology of border walls, travel bans and political incorrectness.

But his career as a political consultant has been short and checkered. As the president has observed, Mr. Bannon did not join Mr. Trump’s campaign until August 2016, by which time Mr. Trump had secured the Republican nomination. Mr. Trump’s general election victory was remarkable. It was also something of a black-swan event. There is a tendency, especially among Mr. Trump’s supporters, to overlook the fact that, had some 79,000 votes in three states gone the other way, the winner of the popular vote would now be in the White House.

Since his inauguration, President Trump’s numbers have steadily declined. He is at 39 percent approval and at 55 percent disapproval in the Real Clear Politics average of polls. The low standing depletes Mr. Trump’s political capital and his leverage over Congress. It endangers Republican control of one or both legislative chambers. Perhaps it is time to take advice from someone else.

Of course, Mr. Trump does not seem inclined to listen to anyone at all. That is even more reason not to exaggerate Mr. Bannon’s influence. Mr. Bannon may have encouraged Mr. Trump to follow his instincts, but that is precisely the point: Mr. Trump’s natural inclinations are in perfect harmony with the voters he refers to in casual conversation as “my people.” Mr. Bannon may have encouraged Mr. Trump not to back down from his positions on the violence in Charlottesville and on the place of statuary memorializing the Confederacy. But the final decision, like all decisions in this White House, was Mr. Trump’s alone.

Mr. Bannon has flitted through an eccentric career in the Navy, on Wall Street, in Hollywood and in the populist faction of the conservative movement. He has a reputation as a well-read autodidact whose syncretic worldview is the result of years of independent and wide-ranging study.