Chinese President Xi Jinping has returned to the country after attending the fourth Nuclear Security Summit in Washington DC. In a keynote speech, President Xi proposed the promotion of international cooperation in nuclear security. President Xi's trip has been hailed as a success by Chinese Foreign Minister Wang Yi, who said that it would help reaffirm China's commitment to promoting mutually beneficial cooperation and safeguarding global nuclear security. Wang said that China had submitted the country's "National Progress Report on Nuclear Security" to the summit, and underlined China's nuclear security achievements. China and the United States also took the opportunity to issue a joint statement on nuclear security cooperation. The two countries have built a Center of Excellence on Nuclear Security in Beijing, which is the largest of its kind in the Asia-Pacific region.So, how can summits like this help to promote nuclear security? What contributions has China made in this area? And how does the nuclear issue fit into the bigger picture of China-US relations?  PIK speaks with Shi Yinhong, Professor of International Relations and Director of the Center for American Studies at Renmin University of China, and Dr. Richard Weitz, Director and Senior Fellow of the Center for Political-Military Analysis, Hudson Institute.