The Democrats will never lose DC. Even if there is another realignment, it will stay with the Democrats, just like Kansas and Nebraska have always stayed with the GOP.
So why do these areas keep sticking with the same party? Many constituencies have changed as the parties have changed. For example, African Americans were heavily Republican until the FDR administration and then became heavily Democratic as a result of the New Deal. The reactionaries of the South used to be heavily Democratic and then turned heavily Republican.