Chinese President Xi Jinping and President Obama at The Hague last year. (Kevin Lamarque/Reuters)

Kenneth C. Brill was U.S. ambassador to the International Atomic Energy Agency from 2001 to 2004. John Bernhard was Denmark’s ambassador to the IAEA from 2005 to 2011.

An initiative to address a persistent and potentially catastrophic threat to global security is a terrible thing to waste. But that is what’s about to happen to President Obama’s effort to prevent nuclear terrorism by securing the world’s most dangerous materials.

In 2010, Obama launched the Nuclear Security Summits to galvanize world leaders on this issue. In Washington that year, Seoul in 2012 and The Hague in 2014, the leaders of 53 countries agreed to steps designed to improve the security of nuclear and other radioactive material. Some 6,000 tons of nuclear material have been permanently secured as a result of the three summits, and participating countries developed other initiatives to strengthen nuclear security practices. But all these initiatives are voluntary; countries are free to implement them or not, as they deem fit.

The summit process is expected to conclude next year, when Obama will again host the gathering in the United States. Early indications are that the 2016 event will lead to the announcement of additional voluntary proposals, along with a declaration that responsibility for further work on nuclear security issues will revert to the patchwork of institutions and mostly voluntary arrangements that predate the summit process, such as Interpol, the International Atomic Energy Agency, the G-8 Global Partnership. and the Global Initiative to Combat Nuclear Terrorism.

This back-to-the-future approach to nuclear security will do nothing to close the long-standing gaps in the nuclear security regime that Obama’s summit process has not addressed. And these gaps create opportunities for terrorists to exploit.

Our global nuclear security regime has gaps because it is fragmented and largely voluntary. For example, there are no binding standards for securing dangerous nuclear material, no process for assessing how states are implementing nuclear security arrangements and no mechanism for reviewing and improving the regime over time.

Many assume that the IAEA performs these functions, but they are wrong. While the IAEA is an important resource, member states created it to provide guidance, not binding obligations. The agency can only recommend security practices. It cannot require or control them.

Nuclear terrorism remains a credible catastrophic threat to global security and prosperity. Indeed, a front-page article in The Post this month reinforced this point, highlighting U.S. concerns that highly enriched uranium in South Africa “could be stolen and used by militants to commit the worst terror attack in history.” Meanwhile, as global demand for nuclear energy for power production, industry and medicine increases, there will be ever more nuclear material to keep out of terrorists’ hands.

With the summit process drawing to a close, the time has come to develop a global nuclear security regime commensurate with the threat.

The vital first step in that direction would be negotiating the first International Convention on Nuclear Security , a model draft of which was released this week in Washington by the Nuclear Security Governance Experts Group. Such a convention could establish binding standards for securing nuclear and other radioactive material based on the IAEA’s currently voluntary guidance, as well as a process for assessing the implementation of those standards. Most important, a convention could create a mechanism — the Conference of the Parties to the convention — to meet periodically to review and make needed improvements in the regime.

To be clear, a convention would not affect existing obligations or voluntary agreements; it would supplement them by filling the gaps. The work of the Conference of the Parties would strengthen and develop the regime over time and would help the IAEA, not undercut it.

Some will argue that a new global negotiation on nuclear security is impracticable. But a relatively small number of relevant countries could negotiate and bring into force a nuclear security convention and then grow it into a convention with universal membership. The ozone protection treaties followed this route and now deal successfully and universally with another complex global threat rooted in technology.

Obama showed vision in launching the Nuclear Security Summits in 2010, but they have not produced the robust and durable security regime needed to prevent nuclear terrorism. Work needs to begin now so that the 2016 summit can establish a group to negotiate an International Convention on Nuclear Security. Otherwise, the legacy of the summits could end up being the persistence of holes in a patchwork security regime — and the possibility that terrorists could find a way to slip through them.