U.S. Park Police officers arrest demonstrators in front of the While House on Thursday. They were protesting against a proposed 1,700-mile-long pipeline that would carry oil from the tar sands in Alberta, Canada, to the U.S. Gulf Coast. Maggie Starbard/NPR hide caption

itoggle caption Maggie Starbard/NPR

President Obama speaks in the Rose Garden on Wednesday, flanked by U.S. Chamber of Commerce Chief Operating Officer David Chavern (left) and AFL-CIO President Richard Trumka (right). Business groups and unions are just two of the groups Obama will try to please with his jobs plan next week. Evan Vucci/AP hide caption

itoggle caption Evan Vucci/AP

Cmdr. Andrew Smith with the Los Angeles Police Department helps enforce a city ordinance that cracks down on illegal animal sales. Gloria Hillard for NPR hide caption

itoggle caption Gloria Hillard for NPR

A lab technician prepares blood samples from volunteers for viral genotyping at a government-run health center in Bagamoyo, Tanzania, in 2009. Tanzania is currently hosting the final stages of a human trial of a pioneering vaccine against malaria. The vaccine is one of many medical innovations to emerge from Walter Reed over the decades. Tony Karumba/AFP/Getty Images hide caption

itoggle caption Tony Karumba/AFP/Getty Images