Despite all that Barack Obama has to preoccupy himself with in Afghanistan and Iraq these days, it is Iran that is likely to be the U.S. president's most serious foreign policy-challenge in the coming months. By now it is clear that Iran is headed toward nuclear weapons -- and that's plural weapons, not just one. Iran's goal is a nuclear weapons arsenal. The only question that remains is whether this will be maintained for deterrence and regional power politics or actually used. That answer will depend on the balance of power within the Iranian leadership.

Obama essentially has two options: He can provoke the Iranian leadership, or he can seek to influence it, tipping the balance in favor of the moderates. The options mentioned in policy circles so far include striking Iran, supporting an Israeli attack, or imposing ever more stringent sanctions. None will work, however, and each will backfire -- empowering the regime's most radical elements by offering them a pretext to attack Israel or the West. The president must resist the temptation to use highly visible, but blunt instruments of power.

Instead, the Obama administration must work to isolate the religious fanatics and their allies among the Revolutionary Guards, empowering the moderates. Elements of such a strategy include: increasing economic and cultural openness toward Iran; coordinating closely with foreign partners, from Europe and Turkey to Russia and China; and aligning NATO's missile-defense plans with its erstwhile rival, Moscow. There is no guarantee, of course, that this strategy will succeed. What it does ensure is -- at the very least -- that the United States will not make matters worse by throwing a public-relations softball to Iran's radical fanatics. Iran's bomb may be inevitable; its use is still preventable.