Mexicans now established in territories previously belonging to Mexico, and which remain for the future within the limits of the United States as defined by the present treaty, shall be free to continue where they now reside or to remove at any time to the Mexican Republic, retaining the property which they possess in the said territories, or disposing thereof and removing the proceeds wherever they please without their being subjected on this account to any contribution, tax, or charge whatever.

Those who shall prefer to remain in the said territories may either retain the title, and rights of Mexican citizens or acquire those of citizens of the United States; but they shall be under the obligation to make their election within one year from the date of the exchange of ratifications of this treaty; and those who shall remain in the said territories after the expiration of that year without having declared their intention to retain the character of Mexicans shall be considered to have elected to become citizens of the United States.

In the said territories property of every kind now belonging to Mexicans not established there shall be inviolably respected.  The present owners, the heirs of these, and all Mexicans who may hereafter acquire said property by contract shall enjoy with respect to it guaranties equally ample as if the same belonged to citizens of the United States.

The ninth article of the treaty is in these words: 

The Mexicans who, in the territories aforesaid, shall not preserve the character of citizens of the Mexican Republic, conformably with what is stipulated in the preceding article, shall be incorporated into the Union of the United States and be admitted at the proper time (to be judged of by the Congress of the United States) to the enjoyment of all the rights of citizens of the United States according to the principles of the Constitution, and in the meantime shall be maintained and protected in the free enjoyment of their liberty and property and secured in the free exercise of their religion without restriction.

It is plain, therefore, on the face of these treaty stipulations that all Mexicans established in territories north or east of the line of demarcation already mentioned come within the protection of the ninth article, and that the treaty, being a part of the supreme law of the land, does extend over all such Mexicans, and assures to them perfect security in the free enjoyment of their liberty and property, as well as in the free exercise of their religion; and this supreme law of the land, being thus in actual force over this territory, is to be maintained until it shall be displaced or superseded by other legal provisions; and if it be obstructed or resisted by combinations too powerful to be suppressed by the civil authority the case is one which comes within the provisions of law and which obliges the President to enforce those provisions.  Neither the Constitution nor the laws nor my duty nor my oath of office leave me any alternative or any choice in my mode of action.