There is a known bug on all platforms where, if you do not exit Galaxy News Radio via the back door as Three Dog instructs, you will be unable to return to the building to complete the quest via the front door (using the intercom will result in the doorman telling you that it's open, when it's not), and the side-door will be locked and require a successful very hard lockpick to open. You cannot backtrack to GNR from Dupont Circle. The back door to GNR is up a destroyed flight of stairs and cannot be accessed. Picking the very hard side door will result in negative karma, but will allow you entrance to the building to complete this quest. This bug can also be triggered by bypassing GNR entirely and going straight to Rivet City, then the Jefferson Memorial. This bug appears to be fixed in the patch.