Complex sentence: In March, 2008, after Democratic Mayor Driscoll announced he would not be running for the seat, Maffei was virtually assured of the Democratic nomination, and ran unopposed in the Democratic primary on September 9th.
Split into simpler sentences: In March, 2008, Mayor Driscoll announced he would not be running for the seat, effectively handing the nomination to Maffei. He ran unopposed in the Democratic primary on September 9th.