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. Jackson, the agency's first black administrator, was constantly caught between White House pledges to solve controversial environmental problems and steady resistance from Republicans—Mitt Romney called for her firing during the campaign, and the House Energy Committee's GOP chair said she'd need her own parking spot at the Capitol because he planned to bring her in for questioning so frequently.
Jackson, 50, a chemical engineer by training, did not point to any particular reason for her departure. Historically, Cabinet members looking to move on will leave at the beginning of a president's second term. "I will leave the EPA confident the ship is sailing in the right direction, and ready in my own life for new challenges, time with my family, and new opportunities to make a difference," she said in a statement. President Obama thanked Jackson for her "unwavering commitment" to public health, calling her "an important part of my team." (Read more Environmental Protection Agency stories.)