I live in Washington DC, yet all of my flights depart or arrive in all airports along the Northeast Corridor from WAS to NYP, including some that Amtrak don't connect to, but in DC you can still get to via public transport like DCA and IAD (Metro and/or Washington Flyer). I also use Amtrak Northeast Corridor for flights out of JFK, connecting at New York Penn Station with MTA Long Island Railroad.