All officers swear an oath to protect and defend the Constitution, not the occupant of the White House. And active duty officers are indeed removed from political activities.
But once an officer of the regular armed forces is shifted from the Active List to the Retired List he can fully and honorably exercise his First Amendment right of free speech.
Should a group of retired officers choose to exercise their First Amendment rights in defense of the Constitution as these have done, their actions should be praised, not deplored.
If the General feels these officers have in any way violated the law, he can recall them to active duty and institute Court Martial proceedings. But this will not happen because the General is wrong.
Must be hell to be a lickspittle for that illegal alien in the White House!