To the House of Representatives of the United States:
In answer to the resolution of the House of Representatives of the 17th instant, requesting the President "to communicate, if not inconsistent with the public interests, copies of all instructions given to the Hon. Ambrose H. Sevier and Nathan Clifford, commissioners appointed to conduct negotiations for the ratification of the treaty lately concluded between the United States and the Republic of Mexico," I have to state that in my opinion it would be "inconsistent with the public interests" to give publicity to these instructions at the present time.
I avail myself of this occasion to observe that, as a general rule applicable to all our important negotiations with foreign powers, it could not fail to be prejudicial to the public interest to publish the instructions to our ministers until some time had elapsed after the conclusion of such negotiations.
In the present case the object of the mission of our commissioners to Mexico has been accomplished. The treaty, as amended by the Senate of the United States, has been ratified. The ratifications have been exchanged and the treaty has been proclaimed as the supreme law of the land. No contingency occurred which made it either necessary or proper for our commissioners to enter upon any negotiations with the Mexican Government further than to urge upon that Government the ratification of the treaty in its amended form.
JAMES K. POLK.
James K. Polk, Special Message Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/201668