The momentum to prevent nuclear terrorism has slowed in the United States, as well. The bitterness in Congress, the lack of cooperation, and the budget sequestration have been responsible for large reductions in spending on nuclear-security programmes. The amount of money that will be saved this year by cutting these programmes – about $340 million – is equivalent to 0.06 per cent of the 2015 defence budget. These short-term savings could prove to be expensive in the long run.

The number of nuclear weapons has declined precipitously since the end of the Cold War, and the physical security of nuclear materials has been much improved. The fact that an act of nuclear terrorism has not yet occurred may be due to the complexity of mounting such an attack, the effectiveness of counterterrorist efforts, a fear of the potential backlash, or a general lack of interest among terrorist groups that might have the capability to commit one. But the fact that it hasn’t happened does not mean it won’t. There are still about 16,000 nuclear weapons in the world. Terrorists only need to steal one. And there’s about three million pounds of weapons-grade uranium, as well as about a million pounds of plutonium, stored at hundreds of different locations. As long as these fissile materials exist somewhere, so will the threat that a terrorist might get hold of them. An improvised nuclear device with one-fifteenth the explosive force of the Hiroshima bomb, detonated at a certain time, at a certain urban location in the United States, could kill about 200,000 people. A nuclear device with two-thirds the explosive force of the Hiroshima bomb, detonated at a certain American port, could kill about 60,000 people, force the evacuation of about six million, and cause about $1 trillion worth of property damage.

The loss of life and economic harm caused by a single nuclear detonation in the United States would cause profound social and political changes. Having destroyed one city, a terrorist group could claim to have other nuclear devices hidden in other cities. The restrictions on civil liberties that followed 9/11 will seem trivial compared to those likely to be adopted after an act of nuclear terrorism. Last year marked the tenth anniversary of the 9/11 Commission Report, which tried to explain how nineteen men armed only with knives and box cutters destroyed two of the largest, most iconic buildings in the United States. I recently asked Lee H. Hamilton, a co-chairman of the 9/11 Commission, whether the threat of nuclear terrorism has been exaggerated. Hamilton is a former chairman of the House Intelligence Committee, with the manner of a solid and sober Midwesterner. He thinks acts of nuclear terrorism are the greatest national-security threat that America faces today. And he cannot understand the complacency in Washington. ‘I don’t get any sense of urgency about nuclear terrorism,’ Hamilton said. ‘What the hell are we doing, that’s the question I keep asking.’

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