If the American citizen takes up arms against the United States, don’t they become a legitimate target?
Please recite the Second Amendment to yourself and ask that same question again. Do you realize what you are saying?
>If the American citizen takes up arms against the United States, don’t they become a legitimate target?
Not necessarily; it depends on if you’re defining it as the institution itself (which surely is) OR as the _people_ [holding offices] of the institution (which EVERY member of the armed forces is possibly required to do under oath or affirmation).