It's a timely message in the wake last Tuesday's attacks in Belgium, which have been claimed by the Islamic State group, commonly known as ISIS or ISIL. But some in the nonproliferation community are concerned that when the summit shuts down at the end of the week, the issue of securing fissile material will cease to be a prime focus for the nations.
Speaking hours after the attacks, Rose Gottemoeller, undersecretary of state for arms control and international security, laid out the stakes clearly: "Nothing I can say would highlight [the summit's message], sadly, better than this tragic attack in Brussels this morning. Thank god those terrorists do not have their hands on nuclear materials."
The Obama administration launched the first NSS, also held in Washington, in 2010. It was followed by a conference in Seoul in 2012 and one at The Hague in 2014. The goal of the summits was to elevate concerns about securing fissile material — the highly enriched uranium (HEU) and separated plutonium which could be used in a nuclear terrorist strike — to a head-of-state level.
According to a State Department fact sheet, the countries involved in the NSS have either eliminated or down-blended enough nuclear material for 1,500 nuclear weapons since 2009. It has also confirmed the elimination of 138 metric tons of Russian weapons-origin HEU — enough for 5,500 nuclear weapons — although some of that elimination began prior to the Obama administration.
But significant amounts of nuclear materials remain out in the world. And while ISIS does not appear to have a dedicated nuclear weapons program, there are reports that two of the suspects in the Brussels bombings were involved in a plot involving surveillance of a high-ranking Belgian nuclear scientist, raising the specter of a nuclear attack in Europe.
In a March 21 report from Harvard University's Project on Managing the Atom, a quartet of experts warned that while the NSS has resulted in some gains, the threat of nuclear terrorism remains very real.
"In the two years since the last nuclear security summit, security for nuclear materials has improved modestly," the authors wrote, "but the capabilities of some terrorist groups, particularly the Islamic State, have grown dramatically, suggesting that in the net, the risk of nuclear terrorism may be higher than it was two years ago."
Those concerns were echoed at a March 23 event by Matthew Bunn, one of the authors of the Harvard study, who noted the "key question this summit has to address is will they take enough action to put a world on a path toward continuously improving nuclear security, even after we're not meeting at the summit level anymore."
Kenneth Luongo, president and founder of the Partnership for Global Security, added that the discussions cannot be allowed to "fall back to the technocrats."
"That's where we were in 2010, and if that's where we end up in 2016, that's going to be a major mistake in my opinion," Luongo said. "So continuing political engagement is absolutely critical, in my view."
Once the NSS concludes, the discussions on nuclear security it fostered will be divided among five tracks led by the United Nations. The others are the International Atomic Energy Agency (IAEA), INTERPOL, the Global Initiative to Combat Nuclear Terrorism, and the G-7 Global Partnership Against the Spread of Weapons and Materials of Mass Destruction.
"I don't have much hope that they're going to deliver a whole lot after the summit process is over. They are five very different, different organizations," Luongo said. "I'm sure there is some value there, but there is nothing that will require any institution to take the recommendations of this summit and institute them."
Another threat to the progress made through the NSS structure is the deteriorating relationship between the US and the world's other nuclear superpower.
After attending the previous three summits, Russia announced it would not be attending this year's event.
"I don't understand myself why they decided they didn't want to come to the summit itself, because we continue to work together so well, and Russia has obviously taken a very responsible role worldwide to try and wrestle with these problems," Gottemoeller said, citing how even in 2015 the US and Russia were able to work together to remove uranium from Uzbekistan.
She added that she doesn't think Russia's disinclination to attend the NSS will affect future nonproliferation efforts between the two nations. But while acknowledging that Russia continues to take part in some effort, Reif did raise a red flag about the lack of Russian presence.
"It's important that Russia be engaged in this high-level process. We have seen in recent years not only the Russian decision not to attend the summit, but Russia's decision to end most nuclear security cooperation that was focused on the security of Russian nuclear materials," he said. "The decision not to attend has been part of a concerning trend on the part of the Russians regarding their overall commitment to continuously improving the nuclear material security."
Aaron Mehta was deputy editor and senior Pentagon correspondent for Defense News, covering policy, strategy and acquisition at the highest levels of the Defense Department and its international partners.