Waiting until the last minute so her seat can be filled by a "properly" vetted replacement. Same with Obama's IL seat back in 2009. Although I don't recall when he put his resignation in.
Manassas airport is home to a defense contractor flying military-type missions in overseas locations. Dynamic Aviation.
This particular flight path looks like ground mapping or LiDAR mapping. Most likely testing a sensor or testing an aircraft.
Washington Center Air Traffic Control (ARTCC) was shutdown due to what is called an ATC-0 event (unplanned closure) due to COVID. Flights can't go into or out of airspace when this happens. Doesn't seem like anything nefarious.
Article here
Required weekly test. Link is here
https://emergencyalertsystem.fandom.com/wiki/Required_Weekly_Test
More information here
Forces can be also supplemented by troops at Ft Belvoir, Marines down in Quantico and troops and sailors from Bethesda possibly