If you could slightly alter the borders of any U.S. state, what would you do? (No counties, just smaller areas).
I would do a few things:
-Move Reagan Airport from Virginia to D.C.
Maryland's charter defined the southern shore of the Potomac as the boundary between Virginia and Maryland. The reason Maryland wanders off to the west and then abruptly stops, is because that is where the Potomac ends (Virginia used to claim southwestern Pennsylvania including Pittsburgh.
So when the District of Columbia was formed, Maryland ceded the area northeast of the river, and the river itself; while Virginia ceded the area southeast of the river. Congress later ceded the Virginia portion back, forming what was then Alexandria County. The city of Alexandria was incorporated and later became an independent city. Alexandria County was later renamed Arlington County, and Alexandria has annexed into Fairfax County.
There have been two additional cessions to Virginia. There was a shallow bay or marshy area that was filled in, and thus became land within D.C. but south of the river. This was ceded to Virginia.
And as part of an expansion of National Airport, the airport was extended into the river and a bulkhead built. This was also in D.C., but was ceded to Virginia. National has since become Reagan National.
It would make more sense to retrocede D.C. outside the Mall to Maryland.