It is also wonderful to see the White House and think/pray for our President and First Lady who have indeed brought diginity and honor back to the office and the "People's House".
I never tire of seeing the Monuments, and I've lived here over 25 years now. If you're not into monumnets, there're always the National Archives, the fantastic museums, etc.
Perhaps some of the folks I've pinged will have other ideas for you. Good luck, and welcome to DC - for a day.
Great suggestion. My favorite is the Museum of Natural History, next the Smithsonian