The NYT reports that Mr. McGahn has cooperated extensively with Special Counsel Mueller's team. The story reinforces my impression that Mr. McGahn is doing well in extraordinarily difficult circumstances.
The story implies, however, that the president could have asserted privilege as against the Special Counsel with respect to communications Mr. McGahn had in his capacity as White House Counsel. In re Lindsey suggests otherwise. Since Lindsey the Seventh and Second Circuits have divided on the question whether a state government official may assert privilege as against a federal investigation. Partly by analogy to control of the corporate privilege in the event of (for example) a special committee investigation, however, Lindsey strikes me as sound.