Nineteen years ago, I was in Ukraine when the last nuclear warheads, orphaned during the Soviet Union’s breakup, rolled out of the country. As an assistant secretary of Defense at the time, I had worked with Washington colleagues and foreign counterparts to eliminate those nuclear weapons and thus one danger at the dawn of the post-Cold War world. Together — with bipartisan support in Congress led by Sens. Sam Nunn, a Democrat, and Richard Lugar, a Republican — we succeeded.

Today, the Iran deal provides the opportunity to address an even greater nuclear threat. Congress should support it because, once implemented, the deal will remove a critical source of risk and uncertainty in a vitally important but tumultuous region.

"Iran's continued pursuit of an illicit nuclear program and North Korea's rash intimidation after sinking a South Korean navy ship are but the most recent reminders of the real need for effective U.S. missile defenses," write Under Secretary of Defense for Policy Michele Flournoy and Under Secretary of Defense for Acquisition, Technology and Logistics Ashton Carter.

President Barack Obama announced Monday that he has nominated Dr. Ashton B. Carter to serve as Under Secretary of Defense for Acquisition, Technology and Logistics.

Dr. Ashton B. Carter and Ambassador Robert G. Joseph discuss recommendations stemming from recommendations in final report of the review they co-chaired of the Defense Threat Reduction Agency (DTRA) and other DOD efforts to counter weapons of mass destruction.

PDP Co-Director Ashton B. Carter testifies before the Senate Committee on Homeland Security and Governmental Affairs.

PDP Co-Director Ashton B. Carter and the Honorable Robert G. Joseph co-chaired a Review Panel on Future Directions for DTRA Missions and Capabilities to Combat Weapons of Mass Destruction (WMD).

This is the fifth in a series of videos on nuclear terrorism based on Graham Allison's book Nuclear Terrorism: The Ultimate Preventable Catastrophe. In this episode former Senator Sam Nunn, former Assistant Secretary of Defense Ashton B. Carter, and U.S. Undersecretary of State R. Nicholas Burns discuss nuclear proliferation and the bold action it will take to make sure that these weapons never end up in the hands of terrorists, criminals or rogue states.

This report of the International Security Advisory Board (ISAB) offers nineteen recommendations for discouraging a cascade of nuclear weapons states.