Flight
The DMV (D.C., Maryland, Virginia) has 3 airports all approximately the same driving time from our house. Ronald Reagan National (DCA), Dulles International (IAD), Baltimore/Washington International (BWI). I would pick whichever airport is cheapest for you!
Hotel
Working on a hotel block. Details to follow
Train
From Ronald Reagan National (DCA) you can take the Yellow line to Gallery Place Chinatown and then take the Red Line to Bethesda (approx. 50 mins). The Bethesda metro is within walking distance of downtown.