The International Atomic Energy Agency reported last week that Iran has a sufficient quantity of enriched uranium to make two nuclear weapons with relatively little further enrichment. While Iran denies that its nuclear program is a weapons program, both classified and unclassified evidence irrefutably rebuts its contention. The need for a realistic look at this situation and long overdue hard policy choices are before us.

Even without nuclear weapons, Iran continues to engage in military aggression both directly and through proxies against its “enemies.” Those include Israel, peaceful people in Lebanon, the U.S. in Iraq, Afghanistan, and Saudi Arabia. It seems plain that Iran’s aggression will escalate substantially following its acquisition of nuclear weapons, at least under the current Iranian regime.

Iran’s pursuit of a nuclear weapon capability and its aggressive projection of power in the Middle East already have affected the region. The Gulf Cooperation Council, which includes Saudi Arabia, has announced a project to develop “nuclear energy” programs. Leaders of the countries in the region know that, as one of them said to me four years ago, “someone in the region” will acquire nuclear weapons if Iran develops them.

Arab leaders’ justifiable apprehension, distrust, and even enmity for Iran are enormous. “Someone” among the Arab states surely will acquire nuclear weapons. Saudi Arabia and Egypt will not forgo a defense against escalated Iranian aggression and nuclear intimidation.

As Iran’s nuclear weapons program has progressed and President Mahmoud Ahmadinejhad repeatedly threatened to annihilate Israel. Israel, already a nuclear power—though one that has never mentioned its nuclear weapons, much less threatened to use them, in forty-five years of peace and war—has been on edge. It recently has moved nuclear missile capable submarines to the Persian Gulf.

The likelihood of a limited nuclear war (or a nuke being exploded by Iranian-sponsored terrorists) in the region will be substantial if Iran gets nuclear weapons.

Can a nuclear-armed Iran be contained? The United States and its allies for at least six years have promised tough sanctions that will dissuade Iran from continuing down the path to acquiring nuclear weapons.

But what they have characterized as tough sanctions before and tougher sanctions thereafter have not done the trick. Sanctions that could have persuaded Iran to forgo its nuclear weapons program are those that would have hurt its economy, such as cutting off lines of credit and other banking capabilities of the government and selected businesses and cutting off insurance necessary for shipments to Iran. These are plainly tougher than any sanctions on which the leading countries can agree.

In view of the failure to dissuade and deter Iran from continuing its nuclear program, what can the United States and the rest of the West do to “contain” a nuclear-armed Iran?

What could the United States threaten that would deter Iran and what could it promise to assure Iran’s potential victims in the region that they are not vulnerable to escalation of Iran’s hegemonic aggression and nuclear intimidation? Threaten Iran with more sanctions? Promise more tough diplomacy? Threaten more “serious consequences” if Iran crosses specified “red-lines”?

Is it reasonable to believe that an effective policy of containment would dissuade and deter a nuclear-armed Iran from both escalated aggression and actually detonating a nuclear weapon, and also would assure its potential victims? I think not. A nuclear-armed Iran will dramatically increase chances for nuclear exchanges costing hundreds of thousands of lives.

Consider the history of the world’s major nuclear powers. It took the United States, the Soviet Union, Britain, France, and China decades to learn how to manage nuclear weapons—to weave the possession of these terribly destructive weapons into constructive national security and military doctrine, to make them a force for stability, security, and peace.

There were perilous moments along the way—even “on the brink” moments. The five powers did not want to foment a nuclear exchange. They had second-strike capabilities that deterred adversaries from initiating a nuclear attack. They devised means of reducing the risks—hot line phones, nonproliferation regimes, exchanges of information, inspections, and the like.

Perilous moments in a nuclear-armed Middle East are unlikely to have such unbloody outcomes as those in the Cold War. Iran and other Middle East countries would be tempted to use their limited nuclear capabilities to eliminate the limited nuclear capabilities of their adversaries before their adversaries could use them.

None of them, other than Israel, would have second-strike capabilities providing deterrence and assurance. And Israel’s second-strike capability would be limited because it is so small; its enemy would know that Israel likely could not recover from a first strike and might risk an Israeli retaliatory strike to achieve that.

The risks attendant on Iranian possession of nuclear weapons are so great as to be intolerable. Containment will not work. Consideration of military action against Iran therefore is necessary.

Military action would have bad consequences. It would be accompanied by loss of lives and large expenditures and might not permanently derail Iran’s nuclear weapons program—although it likely finally would convince Iran, and others, of the determination of the US and allies. But the consequences of military action would be less severe than the consequences of Iran being allowed to go nuclear.

Political damage from military action would be great. The leaders of the Arab states would publicly express outrage but privately be pleased by Iran being prevented or delayed in adding nuclear intimidation to its tools of aggression. If the United States and allies acted alone—without any participation by Israel—Arab leaders would not be as vociferous in their public criticism. But this consideration is pertinent only to how action should be structured, not to whether it must be undertaken.

Bad actors always present us with bad choices. Iran is a very bad actor. The choices the United States and its allies have so far made have not been realistic. In effect, these nations have refused to choose when the worsening situation cried out for action.

Generally, when none of the bad choices is made, whether because of hope that the bad actors can be persuaded to abandon their bad ways or because of indecision or otherwise, the bad choices only become worse choices—as has happened here.

Jack David is a senior fellow at the Hudson Institute. He was deputy assistant secretary of defense for combating weapons of mass destruction and negotiations policy from 2004 to 2006. The International Atomic Energy Agency's reports on iran can be found here.