Back to Bochco. Mark-Paul Gosselaar, who played Detective John Clark on Steven Bochco's NYPD Blue from '01 to '05, will rejoin his old boss on the new hit drama, Commander in Chief. The show (and many other produced by Bochco) have difficulties generating interest within the younger viewer demographic. Positive local reception of his shows remain concentrated in much older viewers, with an average age of almost 60.  By A. Long