I often shot the Capitol, Supreme Court, Jefferson & Lincoln Memorials in the 1980's. If I used my view, and tripod, I needed a permit. They were easy to obtain. At the Capitol, it got to the point where I would just call the person who issued the permits. She'd tell me to go ahead. When I was approached by Police, they'd call her, and she'd OK my presence. Same with the NPS, and shooting the monuments. It didn't require a lot of effort....
After the Oklahoma City bombings, things changed a bit. At the Capitol, I was limited in where I could set up, and escorted by an officer. I haven't tried post 9/11, though.