Since this has become public, I would be willing to bet that everyone in the WH has now undergone a second background check. Tradition allows for a lot of people to remain from one administration to the next, perhaps this tradition should either stop or include a fresh background check prior to remaining on staff.
What is troubling to me is that he was a Marine. He has not only brought discredit to himself, but to the Corps. A fit punishment for him would be to turn him over to the Marines.