During the big meeting in the Mural Room towards the end of the episode, there is a fire lit in the fireplace. In S.2 Ep 11 "The Leadership Breakfast (2001)" Josh and Sam try to build a fire in that same fireplace only to find the flue has been welded shut since 1896. This is the same fireplace that was also burning and working fine during the vote scene in S.1 Ep.18 "Six Meetings Before Lunch (2000)". Quite the magical fireplace.
The building labeled as the Russell Senate Office Building is actually the Postal Square Building, three blocks north.