DC was severely damaged during the civil war and is no longer functional enough to serve as the US Capital. Facilities there are being repaired/maintained. Some structures (Pentagon) are mostly intact and partially operational.
All government functions have temporarily been moved to Kansas City, MO. The entire Power & Light district of KC has been subsumed by government functions. The KC Convention Center, City Hall, Spring Center, H&R Block World HQ, Municipal Auditorium, are all operating at stressed capacity trying to run the post-war government.