There have been four major investigations into Russian intervention in the 2016 presidential election and the FBI’s handling of the subject — a 2019 report released by special counsel Robert S. Mueller III, a 2019 Justice Department inspector general report, a bipartisan report by the Senate Intelligence Committee issued in 2020 by a GOP-controlled Senate, and now a 2023 report released by special counsel John Durham. All told, the reports add up to about 2,500 pages of dense prose and sometimes contradictory conclusions.