According to the cbp website;** Land or Sea Travel**: U.S. citizens ENTERING the United States by land or sea are required to present a valid WHTI-compliant document, which include:(see link above). It says nothing about LEAVING. This makes sense when you add the running theory that DC is now considered a foreign country and gives more credence to the idea of the corporation being dissolved.

Update: according to one of my commenters they are still checking but are now checking going in and out. The only thing i can think of that continues to fit the theory above is that they would not want to raise more suspicion about the NG's presence.