Stevens' dissent: can Congress define the militia?
In an email, J. Norman Heath (THE authority on Federal-State pre-emption of militia statutes) points out an interesting thing. Stevens' dissent takes the view that the entire purpose of the 2A was to allow States to form militias independent of Federal control (he makes this point in reply to Scalia's argument that a right limited to enrolled militia would be meaningly as a check on the national government, since it could define who is in the militia).
Stevens argues in fn. 20:
"The Court assumes -- incorrectly, in my view -- that even when a state militia was not called into service, Congress would have had the power to exclude individuals from enlistment in that state militia. That assumption is not supported by the text of the Militia Clauses of the original constitution, which confer upon Congress the power to "organiz[e], ar[m] and disciplin[e] the Militia, Art I sec. 8, but not the power to say who will be members of a state militia."
Heath's extensive study of early Supreme Court case law indicates that the Court found essentially that when Congress acted with regard to the militia, it pre-empted the field, and States at most had the power to enforce the Federal commands and apply the Federal punishments. He points to the one case specifically addressing militia membership, The Mass.
""Organizing" obviously includes the power of determining who shall compose the body known as the militia. The general principle is, that a militia shall consist of the ablebodied male citizens. But this description is too vague and indefinite to be laid down as a practical rule; it requires a provision of positive law to ascertain the exact age, which shall be deemed neither too young nor too old to come within the description. One body of legislators might think the suitable ages would be from 18 to 45 others from 16 to 30 or 40, others from 20 to 50. Here the power is given to the general government to fix the age precisely, and thereby to put an end to doubt and uncertainty; and the power to determine who shall compose the militia, when executed, equally determines who shall not be embraced in it, because all not selected are necessarily excluded.
The question upon the construction of this provision of the Constitution is, whether this power to determine who shall compose the militia is exclusive. And we are of opinion that it is.
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The general government having authority to determine who shall and who may not compose the militia, and having so determined, the state government has no legal authority to prescribe a different enrolment."