DC in a day and managed to even take in a White House tour (Scheduled well in advanced and was the purpose of the trip to DC)
6:55AM - Arrive at DCA on a flight from LGA
7:30AM - Cab from DCA arrives at Lincoln Memorial, giving me time for a brisk walk up the mall taking in the Reflecting Pool, Vietnam Vets Memorial, Constitution Gardens, WW II Memorial, Korean War Memorial, and Jefferson Memorial. (There was probably more but they are ones I remember off the top of my head)
9:10AM - Dropped my backpack at hotel (St Regis) and grabbed a quick bite to eat. Bags and cameras are not allowed in the White House and that is the only reason I even stayed the night in DC, I never travel without my cameras so I needed a hotel room to leave my cameras in.
9:40AM - Arrived at the White House for the tour
10:45AM - Left the White House grounds, went back up to hotel to grab my camera gear.
11:25AM - Arrived at the Washington Memorial, didn't go up due to time.
11:45AM - Arrived at the Air and Space Museum, touched the moon rock and ran back out.
12NOON - Arrived at the Capitol Building, walked around outside and left.
12:45PM - Arrived at the Newseum, stayed until at least 3:30PM, had lunch there.
~4:00PM - Taxi over to Arlington National Cemetery, walked around for about an hour.
~5:00PM - Arrived back at my hotel, got room service and fell quickly asleep.
9:00AM (The following day) - Back on a flight from LGA-DCA.
Was a very busy day with a lot of walking but it was great!