Department of Justice, NASA, and the Court of Appeals are some of the ones hit by the government’s failure to extend around 80 certificates used on the U.S.gov domains. Ows2.usdoj.gov is also on Chromium’s HTTP Strict Transport Security (HSTS) preload list. Both Google Chrome and Mozilla Firefox will automatically hide the warning button allowing users to temporarily ignore the warning and open the website. People who still choose to use websites with expired certificates are exposed to: Personal information at risk from man-in-the-middle attacks. Individual susceptible to fraud and identity theft.
Source: https://www.bleepingcomputer.com/news/security/us-government-shutdown-leaves-its-sites-with-expired-tls-certificates/