https://techcrunch.com/2019/01/11/shutdown-government-websites-https-certificates-expire/
Most major government websites aren’t down or likely to go down any time soon. Most government certificates aren’t set to expire for many more months. Also, any government website hosted on cloud.gov, search.gov or federalist.18f.gov won’t get certificate errors, as these domains automatically renew their certificates every three months with Let’s Encrypt.
Until the government opens up again, don’t expect these websites until then. But depending on how long this shutdown lasts, you can certainly expect things to get a lot worse.