Arch-conservative State Del. Bob Marshall from Prince William County has jumped into the race for the Republican nomination to fill the 10th District U.S. Congressional seat being vacated by the retirement of Rep. Frank Wolf. His primary challenger will be State Del. Barbara Comstock of McLean. On the Democratic side, so far Fairfax Supervisor John Foust, also of McLean, is the main contender. The Republican nominee will be chosen in a Firehouse Primary on April 26 when 10 polling places throughout the district will be set up and run by the GOP.