It’s abundantly clear that Trump was lawless and accepted no limits on his power.
Admiral William McRaven (bio here), retired since 2014, criticized Trump as a civilian. Furious, Trump wanted to recall McRaven to active duty and court-martial him for “disloyalty.”
Same with General Stanley McChrystal (bio here), retired since 2010, based on a false conspiracy theory that “McChrystal was advising Democrats on how to use artificial intelligence to track down and counter Trump supporters.”
Active-duty military officers have been relieved for publicly criticizing a president or his policies (e.g., General John Singlaub, details here), based on the principle that the military is subordinate to civilian authority, and because that behavior raises questions about their willingness to obey the commander-in-chief’s orders.
But that rationale entirely disappears after they leave the military and enter civilian life, where they have the same right to speak out as anyone else. This is simply a case of Trump abusing power to retaliate against someone who criticized him who had every right to do so. Read story here and here.