From Mark Milley wiki:

According to Peril, Milley attended the walk in combat fatigues as he had been summoned away at short notice from a planned visit to an FBI operations center, and immediately departed once he and Esper realized the political implications of the walk, saying that he felt "sick" and was "fucking done with this shit" to Esper.[80][81] As a result, Milley was not present for Trump's photo op at St. John's Church.[80][82] The House Armed Services Committee subsequently requested that Esper and Milley testify before the committee about the military's role in the George Floyd protests, which they did on 9 July.[83][84] Unsent resignation letter