[MamaTexan]

The primary limit is the 10th Amendment, which says that even if there are shadows and penumbras, the federal government is prohibited from interfering.

I respectfully disagree.

While the 10th is a powerful restricting force, the primary limit is not to be found in the addendum, but in the Constitution itself.

Article 1, Section 8, Clause 17
To exercise exclusive Legislation in all Cases whatsoever, over such District (not exceeding ten Miles square) as may, by Cession of Particular States, and the Acceptance of Congress, become the Seat of the Government of the United States, and to exercise like Authority over all Places purchased by the Consent of the Legislature of the State in which the Same shall be, for the Erection of Forts, Magazines, Arsenals, dock-Yards, and other needful Buildings

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IMHO, this is primary source of federal limitation.

But if the government be national with regard to the operation of its powers, it changes its aspect again when we contemplate it in relation to the extent of its powers.
The idea of a national government involves in it, not only an authority over the individual citizens, but an indefinite supremacy over all persons and things, so far as they are objects of lawful government. Among a people consolidated into one nation, this supremacy is completely vested in the national legislature. Among communities united for particular purposes, it is vested partly in the general and partly in the municipal legislatures. In the former case, all local authorities are subordinate to the supreme; and may be controlled, directed, or abolished by it at pleasure. In the latter, the local or municipal authorities form distinct and independent portions of the supremacy, no more subject, within their respective spheres, to the general authority, than the general authority is subject to them, within its own sphere. In this relation, then, the proposed government cannot be deemed a national one; since its jurisdiction extends to certain enumerated objects only, and leaves to the several States a residuary and inviolable sovereignty over all other objects. It is true that in controversies relating to the boundary between the two jurisdictions, the tribunal which is ultimately to decide, is to be established under the general government. But this does not change the principle of the case. The decision is to be impartially made, according to the rules of the Constitution; and all the usual and most effectual precautions are taken to secure this impartiality.
James Madison, Federalist 39

The federal government had 2 distinct functions. To deal with incoming goods and governments of foreign countries, and to act as a city government for the city-State known as the District of Columbia.

NEVER was it given the ability to pass legislation that affected the entire country......NEVER!

[Tublecane]

“The federal government had 2 distinct functions. To deal with incoming goods and governments of foreign countries, and to act as a city government for the city-State known as the District of Columbia.”

That’s not true, and I think you know it. How is it possible you’re not aware it had the power to govern relations between the states, as well?

[Phlyer]

As you said, we'll need to respectfully disagree. There are any number of enumerated powers - the exclusive power to coin money, for example - that go beyond your quotation. Clause 17 deals with a special responsibility over what has become the District of Columbia, but it is not the entire list of responsibilities and authorities for the federal government.

Further, there are amendments and they are as real as the rest of it. We, the People can argue about whether a particular amendment is a good idea just as we can argue about some part of the original document, but they are all part of the Constitution today.

The quotation from Madison is interesting, but again you have overstepped the scope of it. The Federal government has certain powers, and it is precluded (at least on paper) from exercising certain other powers. To use your example, the Federal government has powers in DC that it is not free to exercise elsewhere. When Madison discusses *its* [meaning, the Federal government's] powers, there is already an implication that the reader and writer understand the limitations of those.

But more than that, the Constitution does not start out, "I, James Madison, . . . do hereby ordain . . " His opinion is interesting, but only important if his logic is considered compelling by We, the People as a way to explain the written words. Ultimately, it is *our* law, and he's just another citizen expressing his opinion.