What about a pre-emptive strike of our own, like the Osirak raid? The problem is that Iran's nuclear program is now much more advanced than Iraq's was at the time of the raid. Already the U.S. government has no way of knowing exactly how many sites Iran has, or how many it would be able to destroy, or how much time it would buy in doing so. Worse, it would have no way of predicting the long-term strategic impact of such a strike. A strike might delay by three years Iran's attainment of its goal—but at the cost of further embittering the regime and its people. Iran's intentions when it did get the bomb would be all the more hostile.

Here the United States faces what the military refers to as a "branches and sequels" decision—that is, an assessment of best and second-best outcomes. It would prefer that Iran never obtain nuclear weapons. But if Iran does, America would like Iran to see itself more or less as India does—as a regional power whose nuclear status symbolizes its strength relative to regional rivals, but whose very attainment of this position makes it more committed to defending the status quo. The United States would prefer, of course, that Iran not reach a new level of power with a vendetta against America. One of our panelists thought that a strike would help the United States, simply by buying time. The rest disagreed. Iran would rebuild after a strike, and from that point on it would be much more reluctant to be talked or bargained out of pursuing its goals—and it would have far more reason, once armed, to use nuclear weapons to America's detriment.

Most of our panelists felt that the case against a U.S. strike was all the more powerful against an Israeli strike. With its much smaller air force and much more limited freedom to use airspace, Israel would probably do even less "helpful" damage to Iranian sites. The hostile reaction—against both Israel and the United States—would be potentially more lethal to both Israel and its strongest backer.

A realistic awareness of these constraints will put the next President in an awkward position. In the end, according to our panelists, he should understand that he cannot prudently order an attack on Iran. But his chances of negotiating his way out of the situation will be greater if the Iranians don't know that. He will have to brandish the threat of a possible attack while offering the incentive of economic and diplomatic favors should Iran abandon its plans. "If you say there is no acceptable military option, then you end any possibility that there will be a non-nuclear Iran," David Kay said after the war game. "If the Iranians believe they will not suffer any harm, they will go right ahead." Hammes agreed: "The threat is always an important part of the negotiating process. But you want to fool the enemy, not fool yourself. You can't delude yourself into thinking you can do something you can't." Is it therefore irresponsible to say in public, as our participants did and we do here, that the United States has no military solution to the Iran problem? Hammes said no. Iran could not be sure that an American President, seeing what he considered to be clear provocation, would not strike. "You can never assume that just because a government knows something is unviable, it won't go ahead and do it. The Iraqis knew it was not viable to invade Iran, but they still did it. History shows that countries make very serious mistakes."

So this is how the war game turned out: with a finding that the next American President must, through bluff and patience, change the actions of a government whose motives he does not understand well, and over which his influence is limited. "After all this effort, I am left with two simple sentences for policymakers," Sam Gardiner said of his exercise. "You have no military solution for the issues of Iran. And you have to make diplomacy work."