I was talking to a friend who's recently been to DC. I asked her what she did with her purse/backpack when they toured the White House. She said they put them in the Smithsonian Museum lockers. She said they all have them and they're free!
So far, I haven't read that in my guidebook. Is this true? I know I will want my camera, etc., after I take the tour(s) and I don't want to have to travel all the way back to my hotel to get my stuff.