President Trump and his supporters made headway in accusing the Federal government of violating or endangering attorney-client privilege. They’re not wrong. The attorney-client privilege is recognized by our Supreme Court as one of the oldest recognized privileges for confidential communications. See Hunt v. Blackburn, 128 U. S. 464 (1888). The privilege is intended to encourage "full and frank communication between attorneys and their clients and thereby promote broader public interests in the observance of law and the administration of justice,” the Supreme Court explained in 1982. And, in 1998, the Supreme Court confirmed that attorney-client confidentiality is so important to...