We drove out from Iowa last year for Spring Break.
We stayed in Annapolis, MD one night. We got a room in Historic Inns of Annapolis, which was right across the street from the Maryland State House. it was moderately priced and Old Annapolis is very walkable with good seafood restaurants. There is also a great breakfast restaurant called the Iron Rooster. We toured the US Naval Academy. They have two Heisman Trophies in the fieldhouse as well as David Robinson's Naismith Trophy.
We stayed near Manassas, VA for the rest of our stay. We took the Virginia rail into DC two different days. One day we walked the Mall and visited the Smithsonian Air and Space, Natural History and American History museums. The second day in DC we walked Arlington and got a tour of the Pentagon. If you want to tour the Pentagon, you need to make a request more than a month in advance and submit information for a background check for adults in your group. We thoroughly enjoyed the Pentagon tour. We enjoyed just walking parallel to the mall and seeing all of the buildings for all of the federal agencies.
i would recommend eating at either Jaleo or China Chilcano. They are both Jose Andres' restaurants and near Ford's Theater.
Mount Vernon and the Dulles Smithsonian hangar are near each other and are good to pair together for a day. We drove to those. They both have ample parking. Like others above have stated, these are two of the best attractions in the DC area.
We walked both of the Manassass battlefields with my cousin, a retired Army Colonel and military historian. He said Antietam takes a full day to see.
Our last day in Virginia, we drove the highway through Shennandoah National Park on our way to Monticello. Shennandoah is a leisurely, beautiful drive, Monticello takes about three hours to go through, and is worth the drive down to it.