He was first elected to represent the 19th senatorial district in the Pennsylvania Senate in a special election held on November 7, 1995. The special election was triggered by the August resignation of incumbent Republican Earl Baker, with whom Thompson had previously served on the Chester County Board of Commissioners. Thompson defeated Democrat Sara Nichols (along with Libertarian candidate Thomas McGrady, Jr.) by a relatively narrow margin. Thompson's margin of victory was considered stunningly narrow by many political observers.The Philadelphia Inquirer
