I'm surprised there has been no mention of Delta's long-term plan to exit (or at least severely reduce) flights to/from DCA. I've been flying in and out of DCA for many years, and there is no question DL is cutting back; if I recall there was some discussion of swapping DCA with LGA slots recently? All you have to do is look at the reduction in DCA-DTW flights this year, where the cancelled flights had always been full, to see the trend. So I don't see any scenario where DL would look to add at DCA - only to increase profitability of existing as already mentioned.

I assume that for whatever reason, DL just can't make money at DCA.