A Very Stable Genius: Donald J. Trump's Testing of America by Philip Rucker and Carol Leonnig:
Trump had had his eyes on Kelly for a while. After firing Comey in May, the president had asked Kelly to be FBI director. Kelly had declined, saying he preferred to stay as homeland security secretary, but he had observed to Trump that he had been poorly served by his staff because they had let him fire the FBI director without a Plan B. That conversation stuck with Trump, and the last week of July he asked Kelly to step in as chief of staff. Kelly asked to take the weekend to consider the offer, but the president was too impatient. He tweeted Kelly’s appointment before he had agreed to take the job.
Priebus had been in an impossible position. Despite tireless efforts, he never could managed to assert control over basic White House functions, such as communications and policy development, in large part because of the president’s impulses. Trump never fully empowered Priebus, either, allowing Bannon, Kushner, and Ivanka to operate as independent forces outside the chief of staff’s authority. Priebus complained to friends that he often felt demeaned by the president’s treatment of him. Trump had undermined Priebus by calling him “Reince-y.” When they flew to Priebus’s hometown of Kenosha, Wisconsin, for an April manufacturing event, the chief of staff peered out the window of Air Force One and spotted his home down below. The president mocked him for it. These episodes illustrated what some of Trump’s subordinates considered his cruelty as a manager. He was willing—eager, really—to belittle the people working for him.