George Shea Flinn III, the Democrat whose father is a Republican county commissioner, became a Democratic state senator Friday morning, taking the oath of office from no less than Lt. Governor (and Senate speaker) John Wilder in a ceremony at the Crescent Club. On hand were several legislative dignitaries of both parties, as well as congressman-elect Steve Cohen, whose seat Flinn was selected by the Shelby County commission to fill. The new senator will take to Nashville a venerable leather briefcase once owned by his great-uncle, former U.S. Senator Richard Russell of Georgia.