State of Missouri v. Holland, U.S. Game Warden, 252 U.S. 416.
Mr. Justice Holmes, for the majority:
... If the treaty is valid, there can be no dispute about the validity of the statute under Article I, § 8, as a necessary and proper means to execute the powers of the Government. ...
It is said that a treaty cannot be valid if it infringes the Constitution, that there are limits, therefore, to the treaty-making power, and that one such limit is that what an act of Congress could not do unaided, in derogation of the powers reserved to the States, a treaty cannot do. [this refers to the Weeks-McLean Act of 1913, which was struck down] ...
Whether the two cases cited were decided rightly or not, they cannot be accepted as a test of the treaty power. Acts of Congress are the supreme law of the land only when made in pursuance of the Constitution, while treaties are declared to be so when made under the authority of the United States. It is open to question whether the authority of the United States means more than the formal acts prescribed to make the convention. We do not mean to imply that there are no qualifications to the treaty-making power, but they must be ascertained in a different way. [Here, Justice Holmes begins to make a clear distinction between "normal" acts of Congress and Acts made pursuant to a Treaty] It is obvious that there may be matters of the sharpest exigency for the national wellbeing that an act of Congress could not deal with, but that a treaty followed by such an act could, and it is not lightly to be assumed that, in matters requiring national action, "a power which must belong to and somewhere reside in every civilized government" is not to be found. [With this pronouncement, Justice Holmes declares that powers not found within the Constitution, may be found by an act of Treaty - This is a negation of the 10th amendment, which says in effect: Those powers not enumerated, are forbidden to the central government] ... With regard to that we may add that, when we are dealing with words that also are a constituent act, like the Constitution of the United States, we must realize that they have called into life a being the development of which could not have been foreseen completely by the most gifted of its begetters. It was enough for them to realize or to hope that they had created an organism; it has taken a century and has cost their successors much sweat and blood to prove that they created a nation. The case before us must be considered in the light of our whole experience, and not merely in that of what was said a hundred years ago. [And here we have it - That "Living Constitution" that is the darling of progressives. We don't need to adhere to those old dead words, we can simply reinterpret them in a modern context!] The treaty in question does not contravene any prohibitory words to be found in the Constitution. [but, read on!] The only question is whether it is forbidden by some invisible radiation from the general terms of the Tenth Amendment. We must consider what this country has become in deciding what that Amendment has reserved. [Here, we see the death of the 10th amendment. No amendment need be enacted, merely a Treaty ratified by the Senate, to suborn the Constitution]
Now contrast the above with what Justice Black wrote in
Reid v. Covert:
The obvious and decisive answer to this, of course, is that no agreement with a foreign nation can confer power on the Congress, or on any other branch of Government, which is free from the restraints of the Constitution. ...
There is nothing in Missouri v. Holland, 252 U.S. 416 , which is contrary to the position taken here. There the Court carefully noted that the treaty involved was not inconsistent with any specific provision of the Constitution. The Court was concerned with the Tenth Amendment which reserves to the States or the people all power not delegated to the National Government. To the extent that the United States can validly make treaties, the people and the States have delegated their power to the National Government and the Tenth Amendment is no barrier.
Both Courts are using the assumption that if something is not expressly prohibited, then it is permitted. That is directly at odds with what the 10th amendment says:
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
As long as the Court (and the Congress) hold to the idea that the government can do whatever it wants, as long as it is not "inconsistent" (that is, the Constitution does not expressly prohibit the action) with the Constitution, then we are at peril.
Furthermore, some European countries have substantial arms exporting industries but tight gun controls at home; such countries may purposefully insert "poison pill" provisions into the treaty to guarantee US Senate rejection, allowing them to take a "Tough on Guns" stance with liberal voters while simultaneously keeping the gun factories humming and their labor unions happy. 
