As a member of the National Commission on Terrorist Attacks upon the United States (the “9/11 Commission”), I heard a great deal of testimony about the dangers facing our country and warnings that went ignored. One very clear danger that remains is that of nuclear weapons material falling into the hands of terrorists, like al-Qaida and its affiliates. That group and others pursue plans for many different types of attacks. But there is one type of terrorism that senior al-Qaida members have always been clear about — that it is their religious duty to kill as many Americans as possible, and that the best way to do that is through nuclear terrorism. We must not let that happen.With sequestration, tight budget times and partisan squabbling in Washington, D.C., these days, there is the danger of important programs that secure and dispose of nuclear material will be scaled back or eliminated. We must not let that happen either.The information genie is out of the bottle — how to use nuclear material to build a nuclear device has been broadly known for decades. It is therefore imperative that that material be secured and eliminated. If terrorists can’t get their hands on nuclear materials, there can be no nuclear terrorism. According to a public report by the U.S. Government Accountability Office last year, terrorists could use as little as 18 pounds of plutonium or 55 pounds of highly enriched uranium to construct a crude nuclear device.The report advised that, “Of great concern is that terrorists could fashion a crude nuclear bomb made from either enriched uranium or plutonium into an improvised nuclear device ... Nonproliferation experts estimate that a successful improvised nuclear device could produce the same force as the equivalent yield of the bomb that destroyed Nagasaki, Japan in 1945; it could devastate the heart of a medium-sized U.S. city. The explosion could cause hundreds of thousands of deaths and injuries, as well as pose long-term cancer risks to those exposed to the radioactive fallout.”The United States has taken the lead in the world in eliminating nuclear weapons material. The Highly Enriched Uranium Purchase Agreement with Russia allows the U.S. to buy uranium that formerly was used in Russia’s nuclear arsenal to be burned in American nuclear power reactors. By the time the provisions of this agreement have been completed, more than 550 tons of HEU, equivalent to about 20,000 nuclear weapons, will have been permanently eliminated from the Russian stockpile. The U.S. and Russia also have an agreement for plutonium disposition. The Plutonium Management and Disposition Agreement calls for each country to dispose of at least 37 tons of surplus plutonium from nuclear weapons. That 74 tons of plutonium is enough for approximately 17,000 nuclear weapons. The agreement calls for disposal through mixing typical nuclear reactor fuel, uranium oxide, with plutonium oxide from nuclear weapons, thereby producing what is called mixed oxide (MOX). The process — endorsed by the National Academy of Sciences in 1995 — will change the isotopic composition of the plutonium making it unusable for weapons, whereas other alternatives for disposition would not.The National Nuclear Security Administration is building a MOX facility at the government’s Savannah River Site that will render the plutonium unusable in nuclear weapons or devices and convert it to fuel assemblies that will be burned U.S. nuclear power reactors.Some want to delay this important plutonium disposition, which would be a critical mistake. Every dollar diverted delays the effort to get rid of plutonium, and every delay provides more time for the material to be stolen.Additionally, the HEU Russian purchase program is coming to an end and there are voices against more engagement with Russia.Eliminating these vast quantities of plutonium and HEU will provide a high degree of nuclear security, because the material can’t be stolen and used by terrorists to fashion nuclear bombs. As an added benefit, the huge security costs (up to tens of millions of dollars a year) it takes to guard this dangerous material will be saved. These national security programs have been supported by President Obama and his past two predecessors. They are rare points of agreement between Republicans and Democrats in a polarized political environment.Fissile material disposition efforts must continue — there is too much at stake. It is important that we continue working with Russia and other nations to secure nuclear material. As bad as the 9/11 terrorist attacks were, a nuclear terrorist attack would be far more devastating and the effects would last for generations. I agree with my former Senate colleagues Sam Nunn and Dick Lugar, who have been leaders for decades in nuclear threat reduction, that after a terrorist nuclear attack we would openly wonder what we wished we had done to prevent such an attack — and we need to ask ourselves why aren’t we doing it now? As terrorism becomes a bigger problem, the United States government must remain on guard for all threats. We also must continue to secure and dispose of dangerous nuclear weapons material.It is vital that we continue with the MOX Project to dispose of plutonium, and we need to find a way to renew HEU disposition efforts while minimizing uses for the material. Our children and grandchildren depend on it.Slade Gorton is a senior fellow at the Bipartisan Policy Center, served in the United States Senate from 1981-87 and 1989-2001, and was a member of the 9/11 Commission.