According to a new survey from Politico.com, Democrat Barack Obama is leading Republican John McCain by a sizable margin in St. Louis County.

Sen. Barack Obama holds leads in four key counties that will go a long way toward determining the eventual winner in four important swing states—Missouri, Ohio, Pennsylvania, and Virginia—according to a new Politico/Insider Advantage survey.

Obama is poised to expand on recent Democratic gains in three populous suburban counties—Pennsylvania’s Bucks County, Missouri’s St. Louis County and Virginia’s Prince William County…

Obama also has opened up a wide 53-37 percent advantage over McCain in suburban St. Louis County, which does not include Missouri’s largest city, St. Louis. In 2004, Democrat John Kerry carried St. Louis County, the most populous county in the state, 54-45 percent.