Adam O’Neal, the editor of The Washington Post’s opinion section, is stepping down Aug. 31 after just over a year leading the section through an overhaul directed by owner Jeff Bezos. O’Neal told staff in a memo that the decision was difficult. Under his leadership, the opinion section was reshaped to promote free markets and individual liberties. The move caught the Post’s leadership off guard, according to a person familiar with the matter, who said they were blindsided by the announcement. O’Neal had been brought into the role to champion that new direction, and his departure leaves the section without a named successor.