Medical workers treat Ebola patients at the Eternal Love Winning Africa hospital in Monrovia, Liberia. Three workers at the hospital, including Dr. Kent Brantly (left), have tested positive for Ebola. Courtesy of Samaritan's Purse hide caption

During nationwide polio campaigns, hundreds of thousands of health workers go door to door, giving children two drops of the polio vaccine. Anadolu Agency/Getty Images hide caption

When "Cowboy" Jack Clement died in August 2013, he'd just completed what would be his final album, For Once and for All. J. Niles Clement/Courtesy of the artist hide caption

People holding Ukrainian and Crimean Tatar flags demonstrate in front of the French-built Vladivostok warship in St. Nazaire, western France, on June 1. The protesters are opposed to the sale of the Vladivostok and Sevastopol warships to Russia. Jean-Sebastien Evrard/AFP/Getty Images hide caption

Georgia Democratic Senate candidate Michelle Nunn greets campaign volunteers at South DeKalb Community Achievement Center in Decatur, Ga., on May 13. The U.S. Senate race in Georgia is one of the most closely watched in the country. David Goldman/AP hide caption

A portrait of then-Sen. Warren G. Harding a few years prior to being elected president in 1920. Harding typically ranks near the bottom of U.S. presidents — but a steamy trove of love letters is putting him back in the public eye. Library of Congress hide caption

Lt. Raj Bansal and Capt. Joseph Shannon (right) approach Foxtrot-01, a remote nuclear missile base in Nebraska. Geoffrey Brumfiel/NPR hide caption