You typically won't find a single date on the homepage of WhiteHouse.gov or any other website. At best, there may be a copyright date in the footer, but that's usually generic to the entire site and doesn't actually tell us anything about the date it was last updated.
When we're missing information a citation calls for:
- MLA: just skip over it
- but it's a good idea to add the date you accessed it to the end of the citation!
- APA: write n.d. for "no date" in this case
More to the point, whatever citation style you're using, you typically will not cite entire websites. Individual articles or pages are more likely to have dates.
For example, WhiteHouse.gov prominently links to press releases for the administration, and each of these has a date.
You would write a separate individual citation for each page you borrowed information from, even if they're all on the same domain.
But that doesn't always help, either -- e.g. the page about the White House building does not offer any dates, either. In this case, we follow the guidelines for missing info mentioned above.
