The idea that several American citizens on American soil can secretly be declared enemy combatants, secretly be declared flight risks—or whatever criterion you prefer—and secretly fitted with secret ankle bracelets is simply not realistic. When you have to reach that far to believe a theory, it’s time to question the theory.
You can characterize it as “not realistic,” but that doesn’t carry any weight in a context of constitutional law.
Dealing with existential threats justifies a president declaring something to be classified, or secret. I don’t know if this is what happened, but it sure does refute your comment.
How far is it reaching when people conspire to assassinate a president? I don’t think you can reach any farther than that. And it should be met with the full weight of justice.