by Kevin Freking WASHINGTON (AP) — The Obama administration's chief environmental watchdog, EPA Administrator Lisa Jackson, is stepping down after a nearly four-year tenure marked by high-profile brawls over global warming pollution, the Keystone XL oil pipeline, new controls on coal-fired plants and several other hot-button issues that affect the nation's economy and people's health. FIRST BLACK EPA CHIEF-- This photo April 17, 2012 photo shows Environmental Protection Agency (EPA) Administrator Lisa Jackson during an interview with The Associated Press at EPA Headquarters in Washington. (AP Photo/Kevin Wolf, File)
