Although terrorists who acquire a nuclear device would have many options beyond its outright detonation, the US strategy is to cut off all options by denying them nuclear material and technology in the first place.

Decades before Sochi, the Bulletin had concern that terrorists might obtain nuclear material. 

In a casual, often-irreverent tone, journalist William Langewiesche walked readers of the December 2006 issue of The Atlantic through the possibilities and hurdles associated with procuring the required material for a nuclear weapon, transporting it to a safe place, and assembling the bomb. With no ambitions to provide solutions to these questions, his article was a pretext to draw attention to the successes and failures of U.S.

It's irrational to think that human beings would behave rationally in the hours and days after a nuclear terrorist attack.

If we lose Washington, we better get our story straight. Otherwise, history will rewrite itself.

The US National Security Strategy, released by the White House in May 2010, states that "there is no greater threat to the American people than weapons of mass destruction, particularly the danger posed by the pursuit of nuclear weapons by violent extremists and their proliferation to additional states." This is why the Obama administration is in the midst of an international effort to secure all vulnerable nuclear materials around the world in four years. Republicans and Democrats alike have voiced support for limiting access to vulnerable nuclear materials to prevent nuclear terrorism.

The television drama 24 is currently portraying one of the most frightening and dangerous terrorist scenarios possible--an anti-American terrorist group with radioactive fissile materials intent on detonating a "dirty bomb" in New York City to render it uninhabitable for decades to come. Jack Bauer, the show's intrepid hero, is trying to track down the terrorists and capture the fissile materials before the terrorists have a chance to blow them up. Although television dramas often engage in hyperbole, the basic theme of this terrorist scenario is very real.

An act of nuclear terrorism could involve detonating an atomic weapon, lacing conventional explosives with radioactive material, or attacking a power plant. Each would have different results.

Osama bin Laden's death may represent a significant turning point in the US effort to defeat Al Qaeda, but the threat of nuclear terrorism will not lessen in the wake of his demise. Such threats, however, are preventable, and the United States must now take care to sustain the nonproliferation and threat reduction programs that will help stop terrorists from obtaining nuclear materials.

The presidential candidates must do more than accept the possibility of a terrorist attack with an improvised nuclear device. They need to plan an effective response that reduces the mass morbidity and mortality such an attack inevitably will cause.

China’s nuclear establishment needs a cultural shift.

Earlier this year, four senior statesmen--former secretaries of state George Shultz and Henry Kissinger, former Defense Secretary William Perry, and former Georgia Democratic Sen. Sam Nunn, all veterans of the Cold War--issued a statement in the Wall Street Journal calling for complete nuclear disarmament. It's an attractive vision, but an idea with little political reality.

Remarks of former US Secretary of Defense William J. Perry made at the Bulletin's 70th anniversary Doomsday Clock Symposium in November 2015, in Chicago

The far-right extremist nuclear terrorism threat is amplified today by an ideology focused on accelerating the collapse of society and a documented interest in pursuing nuclear terrorism. Officials need to act decisively to better understand and mitigate this threat.