Remember: If you want to visit your Senator you have to make an appt. in advance. Also, see the Supreme Court. A beautiful majestic building.
Union Station is another neat spot.
I think you will notice how clean it is--I did. Have a good trip.
Forgot one thing. Check out Kennedy's grave in Arlington. Very pretty setting. Viet Naum Memorial is moving. Michelin's pocket directory about DC is excellent and it is easy to carry around.