Sen. Ben Nelson (D-Neb.). Chip Somodevilla/Getty Images hide caption toggle caption Chip Somodevilla/Getty Images The Two-Way Democratic Sen. Ben Nelson Won't Seek Re-Election December 27, 2011 The race for the control of the Senate just got even more interesting. Democrats have 23 seats to defend. Republicans have 10. The GOP just needs a four-seat gain to take control of the chamber.