Karim Sadjadpour writes: The International Atomic Energy Agency’s new report [PDF] 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 [PDF] 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.