Like blackmail, intimidation only works if it is done in secret. Firing upright people after the fact is an admission of guilt.
The thing to remember about Trump, however, is that he has only one interest—to be noticed. He attaches himself to people, either via antagonism or adulation, for the purpose of getting attention, basking in their reflected glow. It is what he and his fans have in common. It’s a mutual admiration/antagonism society. Once the object is removed, the emotion it prompts is gone. In a sense, they are all “out of sight, out of mind” people. Instinct-driven, but vision provides the prompt.
Very likely the Vindman brothers were particularly vulnerable because Trump could remember their names. He does not like wind.