Go to https://flightaware.com/live/ right now, zoom in, and you can see numerous planes around DC. Right this second there's a helicopter flying right across DC in a northerly direction. Of course it's a DC police helicopter, but there are still regular airlines and small aircraft flying around DC.
Uh, 9/11 comes to mind.
.....what do they do when the tower is closed? This is pretty typical.
There is still some traffic destined there:
https://de.flightaware.com/live/airport_status_bigmap.rvt?airport=KDCA
Blue planes are destined there, green ones came from there. Let's see if DAL459 lands there...
If you click the layers button on the top right, you can enable TFR (temporary flight restrictions) and there is indeed one there:
https://files.catbox.moe/amifxa.png
it's number leads to
https://tfr.faa.gov/save_pages/detail_1_1155.html
Planefag said that the restriction is old, and is a speed restriction in the area.
Go to https://flightaware.com/live/ right now, zoom in, and you can see numerous planes around DC. Right this second there's a helicopter flying right across DC in a northerly direction. Of course it's a DC police helicopter, but there are still regular airlines and small aircraft flying around DC.