Scandal-magnet Republican Jack E. Robinson is making a last-minute bid for the U.S. Senate, filing 10,900 signatures with the Duxbury town clerk just before the Tuesday deadline, according to a source close to the campaign. Robinson, who coughed up $100,000 to collect the signatures, will challenge Wrentham state Sen. Scott Brown in the Dec. 8 GOP primary. The winner will move on to the special election in January. “He’s been trying to stay under the radar,” said the campaign source who asked to remain anonymous because Robinson hasn’t officially announced he is running. The state’s Republican party shunned Robinson after...