Want to see the White House and the Pentagon museum?
It takes approximately 5 hours by bus and about 4 hours by train to get from New York to Washington D.C. Train tickets are considerably more expensive than those for the bus. Schedule and prices vary, so please check the Amtrak website for the train tickets, and the Greyhound website for the bus tickets.
There are great one-day tours by CitySights NY. The tour is 12-hrs long, departs from midtown Manhattan at 7am. See the tour details abd book a tour to Washington D.C. online.