To the surprise of no one, it happened via tweet.
McGahn did not know about Trump's tweet before it was sent and had not previously discussed his departure plans with POTUS, though it was open secret in the WH. He was surprised, though attitude was "of course it happened this way." https://t.co/csLnGJ4agm
— Rosalind Helderman (@PostRoz) August 29, 2018