Thanks to great suggestions from others (thank you!), I've started the first of several free space profiles to collect clippings, images and member rosters of Grand Army of the Republic Posts. The first one is the Oliver P. Morton post in Washington, D.C. of which at least 2 WikiTree profiled veterans are members.
If you have a Union Civil War veteran in your family who was in Washington, D.C. in his later years, do double-check the clippings to see if you recognize a name :) I included a few of the surnames below that are prominent from the current clippings I've uploaded.