Some U.S. federal agencies and initiatives are modifying publicly available data and some datasets may not be accessible on their sites at this time. Look for a notice on visible web pages.
For websites/datasets that appear to be inaccessible, check these 2 archives:
Internet Archive: https://blog.archive.org/2024/
Preserving Public U.S. Federal Data: https://lil.law.harvard.edu/blog/2025/01/30/preserving-public-u-s-federal-data/ (data not currently accessible)