 When Pickett tells Armistead that he cannot order Garnett not to  make the charge, he is alluding to the fact that at Kernstown  (1862), when the Virginians were still under command of Stonewall  Jackson, Garnett had been threatened by Jackson with court martial  for cowardice and dereliction of duty and only Jacksons death  stopped the court martial. Pickett and Armistead as Virginians and  friends of Garnett would have known that, hence Picketts  unwillingness to order Garnett to stay behind.