Robert S. Mueller III served as special counsel for the Justice Department from 2017 to 2019. The work of the special counsel’s office — its report, indictments, guilty pleas and convictions — should speak for itself. But I feel compelled to respond both to broad claims that our investigation was illegitimate and our motives were improper, and to specific claims that Roger Stone was a victim of our office. The Russia investigation was of paramount importance. Stone was prosecuted and convicted because he committed federal crimes. He remains a convicted felon, and rightly so. Russia’s actions were a threat to...