Female rebel fighters gather in Syria's northern city of Aleppo on Saturday to protest what they claim was a chemical attack by pro-government forces in a suburb of Damascus. AFP/AFP/Getty Images hide caption

itoggle caption AFP/AFP/Getty Images

President Obama during his news conference Tuesday at the White House. Larry Downing /Reuters /Landov hide caption

itoggle caption Larry Downing /Reuters /Landov

President Obama is expected to nominate Gina McCarthy, currently assistant administrator with the Environmental Protection Agency, to head the agency on Monday. The nomination requires a Senate confirmation. Alex Brandon/AP hide caption

itoggle caption Alex Brandon/AP