According to the MLA Style Center page on Document Legal Works in MLA Style:
The section of the United States Constitution is represented in the Works Cited list as follows:
United States Constitution. Art./Amend. XII, Sec. 3.
The intext citation would follow this pattern:
(US Const. amend. XII, sec. 3)
If a constitution is published in a named edition, treat it like the title of a book:
The Constitution of the United States: A Transcription. National Archives, United States National Archives and Records Administration, 28 Feb. 2017, www.archives.gov/founding-docs/constitution-transcript#toc-article-iv-.
The Constitution of the United States, with Case Summaries. Edited by Edward Conrad Smith, 9th ed., Barnes and Noble Books, 1972.
References to the United States Constitution in your prose should follow the usual styling of titles of laws:
But your in-text reference should key readers to the appropriate entry:
(Constitution of the United States, with Case Summaries)
