"This precedent, though not legal, still has force itself and has been used in several cases, such as integrating southern schools."
Actually, there is no such thing as binding precedent in the case of executive action. If you mean, "They've done it before, several times," then that is true. It does not follow that the executive will see fit to do it again, or that anybody can make him.
As I say, that's just a calculation of cold political realities in a current situation.
For example, Washington and Colorado are currently in open defiance of federal drug law, to the extent of beginning to make provision for licensing the sale of federally prohibited substances.
I think the odds that any President is going to call the militia on them is pretty low.
Talk about crazy stupid leftist states, though, eh?