You can't carry in the Holocaust museum but they will let you lock it up and go in. Also you can carry on the Library of Congress tour but not on the library floor if you are doing research. You can lock it up in the LoC PD station. You can carry in the Washington monument you just have to sign in on the ground floor and sign out when you leave. The Spy museum was fine. Native American museum, Forestry museum and the Natural History Museum are all OK. The rest already mentioned I had similar experiences. I went on 7 week to weekend visits while my wife worked there a few years ago. I did have better experience with wallet badge and ID better than just ID.