I rarely ride a bike in the District, living and working across in Virginia. I have noticed that the center of downtown DC (~50 square block area containing the Capitol area and monuments) can be relatively bike friendly, where drivers are tempered by Police presence, tourists and camera ticketing. But as you go outward toward the city fringes and beginning suburbs, the traffic becomes almost frenzied. I think that dynarider has it correct.

Judicious use of the sidewalk is okay, but I liked the term "guest" applied to bike riders there, deferring to others.