The International Atomic Energy Agency's new report on Iran's nuclear program asserts that Tehran "has carried out ... activities that are relevant to the development of a nuclear explosive device" and that the agency sees "strong indicators of possible weapon development." In other words, the IAEA has finally reached the same conclusions that Israel first reached in 1995. So should we really be worried about an Israeli strike now?

Historically, there has been an inverse correlation between Israeli saber rattling and military action, but senior Obama administration officials consistently confirm in private meetings that they take "very seriously" the prospect of an Israeli attack on Iran's nuclear sites.
Think of it like this: In one way -- and one way only -- the potential of an Israeli military strike on Iran is akin to a Herman Cain presidency. Its likelihood is slim, but the potential consequences are too dramatic to ignore.
Although the precise strategy Israel would employ to carry out such an operation is debatable, its objective -- to avert a nuclear-armed Tehran -- is crystal clear. What's less clear is how Tehran would react and with what aim. Would the Iranian regime be strengthened or weakened internally? Would it respond with fury or restraint?
To probe these questions, the Brookings Institution in late 2009 assembled two dozen former senior U.S. government officials and Middle East specialists for a daylong simulation of the political and military consequences that would result from an Israeli military strike against Iran's nuclear program.
The simulation was conducted as a three-move game, with Israeli, U.S., and Iranian teams, each representing their government's top national security officials. The members of the U.S. team had all served in senior positions in the U.S. government; the Israeli team was composed of a half-dozen experts on Israel, including former senior U.S. officials with close ties to senior Israeli decision-makers; the Iranian team was composed of a half-dozen specialists, including people who had either lived in Tehran or served as U.S. officials with responsibility for Iran.
I had the unenviable task of trying to channel Iran's supreme leader, Ayatollah Ali Khamenei.
The simulation was premised on a surprise Israeli military strike -- absent U.S. knowledge or consent -- on Iran's nuclear facilities, motivated by the breakdown of nuclear negotiations, the ineffectiveness of sanctions, and newfound intelligence of secret Iranian weapons activity. In other words, pretty close to what we have before us now.
Arguably, the strongest argument against an attack on Iran is a question of simple mathematics. According to Israeli estimates, a strike would, at best, set back Tehran's nuclear clock by just two to three years -- but it would likely resuscitate the fortunes of a deeply unpopular, ideologically bankrupt Iranian regime, prolonging its shelf life by another decade or generation. As one Iranian democracy activist once told me, Israel and the United States should "focus less on the gun and more on the bandit trying to obtain the gun." Bombing Iran, he said, would strengthen the bandit, not weaken it -- and only increase his desire to get the gun.
Iran's nuclear sites are purposely built close to population centers, but in the simulation, the Israeli strike managed to cause only a small number of civilian casualties. Nonetheless, one of my immediate reactions was to order Iranian state television to show graphic images of the "hundreds of innocent martyrs" -- focusing on the women and children -- in order to incite outrage against Israel and attempt to convert Iranian nationalism into solidarity with the regime.
To further that goal, we then invited the symbolic leadership of the opposition -- Mir Hossein Mousavi and Mehdi Karroubi (both of whom are now under house arrest), as well as former President Mohammad Khatami -- onto state television to furiously condemn Israel and pledge allegiance to the government. Instead of widening Iran's deep internal fractures -- both between political elites and between the people and the regime -- the Israeli military strike helped repair them.
I asked a longtime aide to Karroubi about the plausibility of the above scenario. He said that an Israeli strike on Iran would be "10 times worse" -- in terms of eliciting popular anger -- than a U.S. strike and agreed that it would likely bring recognized opposition figures in concert with the government, strengthening the state's capacity to respond.
And respond we did. I went into the exercise believing that the Iranian regime's response to an Israeli military strike -- despite many predictions otherwise -- would be relatively subdued, given the regime's fears of inviting massive reprisals. The opposite turned out to be true. Once our nuclear sites were effectively destroyed, we calculated that we had no choice but to escalate and retaliate in order to save face and project power to our own population and neighbors, deter future attacks, and inflict a heavy political cost on Israel.
Perhaps implicitly, the experience of Israel's September 2007 bombing of a Syrian nuclear reactor was instructive. Aside from a feeble official complaint to the United Nations about Israel's "breach of Syrian airspace," there was virtually no reaction from Damascus. As a result, the Israeli attack was met with little international or even Arab condemnation.
We needed to respond in a way that would further enflame the regional security environment, negatively impact the global economy, and make reverberations felt throughout the world. So we played dirty.
One of our first salvos was to launch missiles at oil installations in Saudi Arabia's Eastern Province, as well as stir unrest among Saudi Shiites against their government. Our pretext was that Israel had used Saudi airspace to attack us, though we later found out it did so without Saudi permission. Given Iran's less-than-accurate missile technology, most missiles missed their mark, but some struck home and we succeeded in spiking oil prices enough so that Americans and Europeans filling their cars with gasoline might be irritated by Israel's actions.
We also fired missiles at Israeli military and nuclear targets and unleashed Hezbollah, Hamas, and Islamic Jihad to fire rockets at Israeli population centers. Although few of these missiles reached their targets, the goal was create an atmosphere of terror among Israeli society so its government would think twice about future attacks.
We didn't limit our reaction to just the Middle East. Via proxy, we hit European civilian and military outposts in Afghanistan and Iraq, confident that if past is precedent, Europe would take the high road and not retaliate. We also activated terrorist cells in Europe -- bombing public transportation and killing several civilians -- in the belief that European citizens and governments would likely come down hard on Israel for destabilizing the region.
But, appreciating the logic of power, we stopped just short of provoking the United States. Before the simulation, I'd often heard it said that it wouldn't make much difference whether Israel actually got a green light from the United States to strike Iran, for Tehran would never believe otherwise.
This assessment wasn't borne out in the simulation. The U.S. secretary of state sent us a private note telling us that the Americans did not approve the Israeli strike, and vowed to restrain Israel from attacking further -- if we also exercised restraint. They tried on multiple occasions to meet with us or speak by phone, but we refused. While Washington believed that its overtures would have a calming effect on us, we interpreted them to mean that we could strike back hard against Israel -- not to mention European targets -- without risking U.S. retaliation, at least not immediately.
Given that the simulation was intended to gauge the immediate consequences of an Israeli strike on Iran -- not its long-term impact -- the final results were inconclusive. The intent wasn't to prove either side correct, but to try to understand the decision-making calculus of each side.
Not unlike wars themselves, different actors drew different lessons. Those, like myself, who thought that the costs of an Israeli attack significantly outweighed the benefits, felt the results of the simulation validated their position. In the span of just a few days, our simulation had the Middle East aflame. But those who, prior to the exercise, believed that attacking Iran's nuclear facilities was a necessary risk weren't convinced otherwise.
Yet the reality is that no one -- not even the Iranians -- can say with confidence how they will choose to react once the fog of war sets in. And as for long-term consequences, it's way too murky to say anything but this: It will be ugly.
One of the great American strategic thinkers of the 20th century, former U.S. Ambassador to the USSR George Kennan, spent more than half a century alternatively thinking about how to avert a nuclear war with the Soviet Union and what a nuclear war with the Soviet Union might look like.  
Shortly before he passed away in 2005 at age 101, he reflected on his half-century of experience. "Anyone who has ever studied the history of American diplomacy, especially military diplomacy, knows that you might start in a war with certain things on your mind as a purpose of what you are doing, but in the end you found yourself fighting for entirely different things that you had never thought of before," he said. "War has a momentum of its own, and it carries you away from all thoughtful intentions when you get into it."
"But also, there is a very, very basic consideration involved here, and that is that whenever you have a possibility of going in two ways, either for peace or for war, for peaceful methods of for military methods, in the present age there is a strong prejudice for the peaceful ones. War seldom ever leads to good results."