When they shut down servers instead of keeping them up with a skeleton crew? LOC data services are down and, as far as I can tell, almost all of NASA's web stuff has been taken down. PubMed is available with a skeleton crew.
Joe Hourclé pointed out on some listservs that they were even given guidance to return an HTTP status of 302 which will essentially tell search engines that they're gone forever.
Luckily, a lot of government-funded science data services are run by universities and research labs that already have their funding and will keep working.
What a mess.