Washington is 31 road miles from Annapolis, which is on the coast of Chesapeake Bay; straight line distance to the coast is shorter.
D.C. is also directly on the shore of the Potomac River where it becomes a tidal estuary.
There is a very, very deep rabbit hole here. Because it's late and I have to be up early in the morning, I'll merely point out the entrance [0] and quietly back away...
I know we're not supposed to call Brexit voters thick, but it's difficult sometimes...
As to failure modes, the decline in small and midsize ports generally in favour of huge container ports, Felixstowe etc., also the offshoring of processing either to factory ships (conveniently located beyond the reach of employment law) or distant countries. Quite a few South and East coast places used to have passenger ferry services to Europe and no longer do - Ramsgate, Hull, Great Yarmouth, Folkestone spring to mind but I'm sure there were more.
Fishing ports which now have few fishers left. Long term decline due to overfishing along with Brexit making it hard for them to sell their catch to markets in EU. Grimsby.
The Victorian seaside mass resorts that lost out to cheap foreign holidays. Blackpool.
Places like Cornwall which are full of second homes and outwardly look very nice but mask deep poverty as there is little affordable housing and few food jobs.
Also the definition of coastal is different in the UK, an island with nowhere more than 70 miles from the sea. Washington DC is 85 miles from the Atlantic but still populated by the ‘coastal elite’.