Edit: seems like they respond only on TCP?
It seems like nih.gov nameservers are down – unless my euro-commie IP address is being blocked (which would be weird).
Can someone from the US please check?
ns.nih.gov. 3600 IN A 128.231.128.251
ns2.nih.gov. 3600 IN A 128.231.64.1
ns3.nih.gov. 3600 IN A 165.112.4.230