In February, the Pentagon released a new Nuclear Posture Review (NPR), a comprehensive overview of the nation’s nuclear forces, their disposition, and plans for the future. Here, Belfer Center experts share their assessments of this NPR and the future of America’s nuclear capabilities.

From sharply rising tensions with a nuclear North Korea and decertification of the Iran nuclear deal to China’s growing global assertiveness and the State Department pullback from projecting American values, such as democracy and human rights, around the world, the United States faces urgent national security challenges.

In a panel discussion Monday evening at Harvard Kennedy School (HKS) moderated by MSNBC host Rachel Maddow, former members of President Obama’s cabinet described what they see as a fraying of alliances, a loss of credibility with allies and enemies, a stepping back as a leader on human rights and democracy, and a relinquishment of diplomacy as a critical component of national security.

For the seventh year in a row, Congress has failed to pass a defense appropriations bill in time to start the fiscal year. And for the past four years, the Defense Department and other federal agencies have been struggling with the impact of sequestration, which imposed cuts that were never meant to be implemented, but were supposed to prod both parties to come together and reach a budget agreement. The Defense Department has done its best to manage through this prolonged period of budget uncertainty, making painful choices and trade-offs among the size, capabilities and readiness of the joint force.

The nation cannot allow this to become the new normal.

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.

A key challenge for the next administration's national security leadership concerns the management of investment in the U.S. national security future. In this paper for the Aspen Strategy Group, Dr. Ashton Carter discusses the challenges of defense budgeting and program selection, and the current mismatch between resources and strategy.

Full text of the trip report from PDP's Track II meetings in Taiwan and the People's Republic of China (PRC).

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