This week, Inside USA travels to the coal mines of Illinois to look at America's dependence on coal, and the politics behind the fossil fuel. Just below the surface of this election campaign runs a deep seam of coal. Half of America's electricity is generated by coal, producing 40 percent of the country's greenhouse gases. Leading climate scientists have called for a moratorium on new coal-fired power plants, saying that addressing global warming means addressing America's dependence on coal.