Military Police units from the United States Army Military Police Command provided security and directed traffic at the Nuclear Security Summit on Monday in Washington. Photo by Walter Fick

Military Police guard the perimeter of the Nuclear Security Summit on Monday. Photo by Walter Fick.

President Obama

Police and Secret Service vehicles sit parked outside the Walter E. Washington Convention Center during the Nuclear Security Summit on Monday. Photo by Walter Fick

A protester holds a Tibetan flag in a park across the street from the Nuclear Security Summit. Photo by Walter Fick

Protesters supporting the Free Tibet movement hold banners outside the Nuclear Security Summit as Chinese President Hu Jintao meets with Obama inside the Convention Center. Photo by Walter Fick