From notes taken during a November 21, 1969, telephone conversation between National Security Adviser Henry Kissinger and Secretary of Defense Melvin Laird following the Cleveland Plain Dealer’s publication of photographs of the 1968 massacre by American soldiers of 347 civilians at My Lai, South Vietnam. Last May the State Department declassified 20,000 pages of Kissinger’s telephone conversations, five years after the National Security Archive began legal proceedings demanding their release.

K was calling about the atrocity case: the President wants to make sure L got a game plan. K said it was going to be a terrible mess.…