An Oct. 28, 1985 photo of John A. Walker Jr., being escorted by a federal marshal as he leaves the Montgomery County Detention Center in Rockville, Md., enroute to a federal court in Baltimore. He was ultimately sentenced to life in prison on espionage charges. Bob Daugherty/AP hide caption

itoggle caption Bob Daugherty/AP

This image, posted on a militant website, shows an Islamic State fighter waving a flag from a captured government fighter jet in Raqqa, Syria. The group is well-funded and has gained territory over the past few months; that's raised some concerns in America, although experts say the organization is largely focused on regional goals. AP hide caption

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This handout photo provided by the Office of the Defense Secretary (OSD), taken Aug. 19, 2014, shows a Chinese fighter jet that the White House said Friday conducted a "dangerous intercept" of a U.S. Navy surveillance and reconnaissance aircraft. Uncredited/AP hide caption

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A photo from March 2008 provided by the Hennepin County, Minn., Sheriff's Office shows Douglas McAuthur McCain, who was killed recently fighting alongside Islamic State militants in Syria. AP hide caption

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American Eric Harroun threatened Bashar Assad on Facebook and YouTube. He spent six weeks fighting with a rebel army, a journey that did not end well for him. ABC News/YouTube hide caption

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During a speech at the American Legion's National Convention on Tuesday, President Obama again called the extremist group the Islamic State a "cancer." Charles Dharapak/AP hide caption

itoggle caption Charles Dharapak/AP

Palestinian boys at a damaged building in Rafah, the Gaza Strip, on Thursday. U.S. attempts to broker a comprehensive peace deal have again been shelved as Israel and Hamas have waged their third round of heavy fighting in Gaza in the past six years. Ibrahim Khatib/Barcroft Media/Landov hide caption

itoggle caption Ibrahim Khatib/Barcroft Media/Landov