To the Senate of the United States:
I have received from the committee appointed by the resolution of the Senate of the 14th day of June a copy of that resolution, which authorizes the committee to confer with the President on the subject of the nomination made by him of a minister plenipotentiary to Sweden.
Conceiving it to be my duty to decline the proposed conference with the committee, and it being uncertain when it may be convenient to explain to the committee, and through them to the Senate, the grounds of my so doing, I think it proper to address the explanation directly to the Senate. Without entering into a general review of the relations in which the Constitution has placed the several departments of the Government to each other, it will suffice to remark that the Executive and Senate, in the cases of appointments to office and of treaties, are to be considered as independent of and coordinate with each other. If they agree, the appointments or treaties are made; if the Senate disagree, they fail. If the Senate wish information previous to their final decision, the practice, keeping in view the constitutional relations of the Senate and the Executive, has been either to request the Executive to furnish it or to refer the subject to a committee of their body to communicate, either formally or informally, with the head of the proper department. The appointment of a committee of the Senate to confer immediately with the Executive himself appears to lose sight of the coordinate relation between the Executive and the Senate which the Constitution has established, and which ought therefore to be maintained.
The relation between the Senate and House of Representatives, in whom legislative power is concurrently vested, is sufficiently analogous to illustrate that between the Executive and Senate in making appointments and treaties. The two Houses are in like manner independent of and coordinate with each other, and the invariable practice of each in appointing committees of conference and consultation is to commission them to confer not with the coordinate body itself, but with a committee of that body; and although both branches of the Legislature may be too numerous to hold conveniently a conference with committees, were they to be appointed by either to confer with the entire body of the other, it may be fairly presumed that if the whole number of either branch were not too large for the purpose the objection to such a conference, being against the principle as derogating from the coordinate relations of the two Houses, would retain all its force.
I add only that I am entirely persuaded of the purity of the intentions of the Senate in the course they have pursued on this occasion, and with which my view of the subject makes it my duty not to accord, and that they will be cheerfully furnished with all the suitable information in possession of the Executive in any mode deemed consistent with the principles of the Constitution and the settled practice under it.
James Madison, Special Message Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/205121