Begin the entry with “U.S. Constitution” in italics and follow with a period.
Enter the number of the article you are citing, in the format “Art. XII,” and follow with a comma.
Enter the number of the particular section you are citing within that article, in the format “Sec. 3” and follow with a period. Your entry should look like this: “U.S. Constitution. Art. XII, Sec. 3.