Looking for the most authoritative source for presidential documents? Googling does not work. You should only cite to the Federal Register or the Code of Federal Regulations, not Whitehouse.gov or some other web site. Georgetown’s research guide on Presidential Documents provides direct links to the Federal Register, Code of Federal Regulations, as well as links to historical versions of these authoritative sources.
If you have a question about these sources, don’t hesitate to ask a reference librarian.