Sure. WAS is located only a few blocks from Capitol Hill and the Washington Metro runs right to it.
I'd take the Red Line to Metro Center and switch to Blue or Orange to Smithsonian. You'll come up right in the National Mall and will have your pick of Smithsonian museums. (All Free.) Other Metro stops will get you closer to the Capitol itself or the National Gallery of Art (two buildings) or the White House.
Lincoln Memorial, Vietnam Veterans Memorial, World War II and Korean War Memorial are longer walks from the Smithsonian stop, but if you don't mind a couple of miles round trip in a safe park setting, they're worthwhile. FDR Memorial is good, but a major hike. Cab might be better for that unless you're up for a long walk and weather is perfect.
If you want a cheap meal in the district, which is a pricey place, I like the old Post Office building on Pennsylvania Ave. There's a food court and also a free elevator to the tower of the building, which is very scenic. Shopping mall food, basically, but cheap and predictable. Lots of good places where you can spend more, but if you're out touristing it's fast and easy.
Actual guided tours, probably, but you're so close to such a great spot to go exploring on your own, why bother.