There is very little the that I want to see outside of the Smithsonian.
Seeing an original draft of the Bill of Rights was neat. Amendment 3, "A well regulated militia..."
Lincoln Memorial, Jefferson Memorial, Vietnam Memorial, WW2 Memorial, , Holocaust Museum are all on The Mall. Totally worth seeing. The 7 Smithsonian’s take time but if you have a good pair of tennis shoes you can hack.
Avoid the Capitol and Washington Monument except looking at it and the seeing all the little statues and stuff around them is better than wasting the day trying to get in.
Damm, what Tom is saying going to be Merryland.