The greatest nuclear danger today is not Countdown to Zero‘s nuclear “accident” or “miscalculation” or “madness.” The greatest nuclear danger today, still, like 65 years ago, is nuclear war.

Two weeks before the 65th anniversaries of the atomic bombings of Hiroshima and Nagasaki, followed just six days later by the end of the Second World War, Magnolia Pictures released a new film, Countdown to Zero. It was made by some of the same people who made An Inconvenient Truth, and the filmmakers unapologetically expressed the hope that it would change the game on nuclear disarmament much as their previous film did on climate change.

The film quite shrewdly bases its argument on a single sentence, uttered by President John F. Kennedy nearly half a century ago. In his first speech before the United Nations, on September 25, 1961, the president said, “Every man, woman and child lives under a nuclear sword of Damocles, hanging by the slenderest of threads, capable of being cut at any moment by accident, or miscalculation, or by madness.”

(Damocles was a court sycophant to the 4th Century BC tyrant Dionysius II of Syracuse. When Dionysius invited him one day to come and sit on his powerful throne, Damocles noticed, to his horror, a deadly sword suspended directly above, point down, held only by a single strand of the hair of a horse. In this way, Damocles learned the truth about the life of a ruler in the ancient world — or, as JFK wisely discerned, the life of everyone in the nuclear age.)

Countdown then, quite persuasively, details how, nearly half a century later, those three nuclear dangers remain quite imminent.

It reveals just how close both the United States and the Soviet Union came, more than once, to launching not just one, but perhaps 101 nuclear-tipped missiles — utterly by accident. (The filmgoer is left to guess the likelihood that we can dodge that particular nuclear bullet indefinitely in a world of nine nuclear-armed nations, with perhaps soon more.)

It examines episodes like the Cuban missile crisis in 1962 (and others almost wholly unknown to the public), when miscalculation, misinformation, or misunderstanding brought us to the brink of a civilization-ending nuclear war. (The filmgoer can perform the same exercise here.)

And it illuminates just how many efforts have already been made, by non-state terrorists, to obtain or build a nuclear weapon, transport it to a major world city, and set it off — and just how likely it is that, eventually, somebody is going to pull that off.

However, Countdown neglects to mention a fourth scenario by which the actual detonation of nuclear weapons might come about sometime in the next century, or the next decade, or the next year.

Don’t get me wrong. The film is excellent, especially as a vehicle for growing the nuclear disarmament movement, and preaching beyond the choir. This is a sin of omission, not commission.

But during this week when we commemorate the 65th anniversaries of Hiroshima, Nagasaki, and the end of the Second World War, one is compelled to point out that the scenario the film omits is, ironically, another Hiroshima. Another Nagasaki. Another conscious, intentional launching of a nuclear weapon. Another calm, sober initiation of nuclear war.

Hiroshima and Nagasaki, which were instantaneously obliterated by the American atomic bombs “Little Boy” and “Fat Man” on August 6th and 9th, 1945 (devices perhaps a hundred times less powerful than many of the nuclear weapons deployed in arsenals today), were not, of course, atomic attacks carried out by the “madness” of non-state terrorists. Nor were they “accidents.” Nor were they “miscalculations.”

The White House was not in a panic in August 1945. The orders to dispatch the B-29’s carrying the atomic bombs were not issued in error. President Harry S. Truman and his advisors were not rushed into hurriedly deciding that if we didn’t immediately launch a nuclear attack upon the Japanese, Tokyo would launch a nuclear attack (or, indeed, any kind of an attack) on us.

No, the United States government made a cool, composed, calculated decision that it could bring about a precisely-defined political aim by employing nuclear weapons as an act of war.

And that kind of nuclear eventuality, today, may be at least as likely as the three others described in Countdown to Zero.

After the end of the Cold War, and before its corpse had even grown cold in the grave, the Clinton Administration astonishingly chose not to diminish, but instead to expand the role of nuclear weapons in American national security doctrines. Now these weapons were designated for the first time as “counterproliferants.”

They were to be used not only in retaliation, but as a tool of pre-emption against “rogue states” and non-state actors. And they were to used to prevent them from acquiring not only nuclear weapons, but chemical weapons and biological weapons as well.

The Bush Administration, in its Nuclear Posture Review of December 2001, specifically articulated several scenarios where the United States might employ America’s vast nuclear arsenal. Like the Clinton doctrines, many of these would be carried out not only not in response to a nuclear attack, but indeed not in response to any attack upon us at all. The Bush document even named seven particular states as the possible targets of a preemptive American nuclear attack upon them.

The Obama Administration, in its Nuclear Posture Review of April 2010, stated plainly that it anticipated far fewer contingencies where the United States might actually use its nuclear weapons in combat.

However, many nuclear policy experts had urged the new Administration to adopt an explicit policy of “No First Use” — a statement that our country would never employ nuclear weapons except to retaliate for the use of nuclear weapons against our allies or ourselves.

China, despite laughably less powerful military forces than the United States, both conventional and nuclear, has long maintained such a policy of “No First Use.”

But President Obama refused. His Administration insists that still, in certain circumstances, the president of the United States might need to authorize an American nuclear first strike. His Administration explicitly maintains the policy option for America to start a nuclear war.

In addition, for at least the past half decade, speculation has run rampant that either the United States or Israel, or both, might launch a preemptive attack on all elements of the Iranian nuclear complex, to forestall the (hypothetical) future possibility that Iran might someday obtain a nuclear arsenal of its own. Just this month, on Sunday August 1, the lead article in the Washington Post Sunday Outlook section, by Steven Simon and Ray Takeyh, was called, “A Nuclear Iran. Would America Strike to Prevent It?”

Such a preemptive strike, of course, might be undertaken exclusively with conventional military forces. Or, it might not.

In the April 17, 2006 issue of the New Yorker magazine, investigative journalist Seymour Hersh alleged that to prevent Iran from acquiring nuclear weapons perhaps 5-10 years down the road, Pentagon planners were preparing not just military strikes on that country, but nuclear strikes.

In the July 10, 2006 issue, Hersh reported that after lengthy and heated internal military debates, the Pentagon brass had concluded that, for the time being, a nuclear attack on Iran would be “politically unacceptable.”

But then on January 7, 2007, the Times of London reported that Israel had begun laying the groundwork for a series of nuclear strikes on the Iranian nuclear infrastructure — perhaps utilizing tactical nuclear weapons supplied by the United States, and perhaps too in conjunction with American forces.

If all that were not worrisome enough, in a CNN presidential debate on June 5, 2007, no less than four of the Republican presidential candidates indicated that to forestall a nuclear Iran, they would consider launching an American nuclear first strike against Iran.

But that all took place during the last Administration, right? Right. But in the press conference announcing the Obama Nuclear Posture Review on April 6, 2010, Secretary of Defense Robert Gates, asked directly about “No First Use,” said that the Administration was unwilling to “limit ourselves so explicitly.”

And when asked directly about Iran and North Korea, he said that despite the limitations on American nuclear employment doctrines in the new document, with regard to those two states in particular, “all options are on the table.” Live on C-Span. Three separate times.

Accident. Miscalculation. Madness. The creators of Countdown to Zero are quite correct in asserting that these contemporary nuclear perils are quite real, and, indeed, that they could come to pass today “at any moment.”

But all the nine nuclear-armed nations must also embrace the principle that nuclear weapons can serve no purpose other than to deter the use of nuclear weapons by others (a purpose that will disappear if, someday, we can achieve at last universal nuclear disarmament).

The nuclear-armed nations cannot continue to conjure contingencies for employing nuclear weapons on any hypothetical field of battle, or to fantasize that starting a nuclear war could ever serve either their own national interests or the interests of the human community.

If they do continue to do so, then we may just be on a countdown not to nuclear zero, but to something else nuclear entirely.

After all, said President Kennedy, in the very next sentence he uttered after his “nuclear Damocles” at the United Nations on September 25, 1961, “The weapons of war must be abolished, before they abolish us.”