Saw an earlier post reference crossing the Potomac on January 6th. As someone that used to live on the Potomac, this is a very very bad idea in any capacity. Aside from it being one of the most heavily guarded areas in all of DC with the Pentagon and Reagan Airport nearby, Coonman and Bowser will likely close all 5 bridges into the District. Maryland is a different story on the other hand. Of all the four quadrants in DC, Northwest is the only one that is not a complete shithole and Maryland shares its border. I would recommend entering through the Chevy Chase area as this is an upscale and almost purely residential neighborhood. Police presence will not be nearly as concentrated there as it will be in Southwest DC. Once you're in Chevy Chase, I would recommend using Massachusetts Avenue or Connecticutt avenue to get downtown. These roads are roads that residents use to get home from their jobs and not well known by tourists. Once you're downtown you know what to do.
P.S.: Do not use I-495, "The Beltline". Typically it is teeming with police looking for speeders and drunk drivers, however they will be looking for something else on 1/6.
Spez: Typos
I wouldn't recommend it since you will likely have to let the city know where you are docking your boat. Also Bowser can close both the Wharf and the Georgetown Marina if she chooses. If you do it, I would one rent one far away from DC and sail it in.