In arguing that the United States has achieved nuclear primacy and thereby made mutual assured destruction obsolete, Lieber and Press rely on some questionable assumptions about the status of Russia's strategic forces.

To make their case that the Russian strategic nuclear arsenal "has sharply deteriorated," Lieber and Press quote statistics showing that Russia today has "39 percent fewer long-range bombers, 58 percent fewer ICBMs, and 80 percent fewer SSBNs [ballistic-missile-launching submarines] than the Soviet Union fielded during its last days." These numbers are generally correct, but a similarly one-sided examination of U.S. forces would have painted a similarly dire portrait; after all, the U.S. nuclear arsenal today has 66 percent fewer strategic bombers, 50 percent fewer ICBMs, and more than 50 percent fewer ballistic missile submarines than it possessed during the Cold War.

Lieber and Press claim that Russia's strategic bombers "rarely conduct training exercises," implying that Russia's military is neglecting strategic aviation. Yet Russia's strategic air forces participated in four major exercises in 2005 alone. Similarly, Lieber and Press refer to a number of failures during launches of submarine-launched ballistic missiles (SLBMs) in 2004 to illustrate the decline of the Russian navy. But they do not mention the much larger number of successful launches or the Bulava SLBM development program, which has been quite successful so far.

It may be true, as Lieber and Press write, that "over 80 percent of Russia's silo-based ICBMs have exceeded their original service lives," but regular and successful tests of ICBMs that have been kept in silos for 25 years or longer suggest that this has not affected the missiles' reliability. Russia is decommissioning its ICBMs not because they are unreliable but because it does not need them. Lieber and Press claim that the development of the next-generation Russian ICBM, the Topol-M, has been "stymied by failed tests." But of 15 flight tests conducted to date, only one has failed -- a remarkable achievement for any missile-development program. It is true that the production rate of new Topol-Ms is low, but that may be because Russia has decided to concentrate on producing the mobile version of the missile, which it will begin deploying this year.

Lieber and Press are right to state that Russia may end up having as few as 150 land-based missiles by the end of the decade. But about half of those ICBMs would probably be road-mobile Topols and Topol-Ms, which, if operated properly, would have a good chance of surviving a first strike. Lieber and Press dismiss Russia's mobile missiles by saying that they "rarely patrol." In reality, very little is known about Russia's mobile-missile patrol rates, and although it is quite plausible that they are low, it is a stretch to assume that they are zero.

Lieber and Press describe Russia's early warning system as "a mess." In fact, although the system is past its prime, it has lost surprisingly little of its effectiveness. It may seem counterintuitive, but Russia would gain very little were its early warning system to be deployed to the fullest extent. Adding the capability to detect SLBM launches would not dramatically increase the time available to the Russian leadership for assessing attacks. The much-discussed "gaping hole" in the radar coverage east of Russia also should be put in context. Missiles launched from the Pacific could not cover the entire range of Russian targets that would need to be destroyed in a first strike. The scenario that Lieber and Press postulate, in which "Russian leaders probably would not know of the attack until the warheads detonated" because of flaws in their early warning system, is simply impossible.

Given Tehran's defiant response to the European and American effort to constrain its nuclear program, it is time for bolder diplomacy out of Washington. U.S. President George W. Bush should take a page from the playbook of Ronald Reagan, who negotiated with an evil Soviet regime--competing in the war of ideas, but addressing the enemy's security concerns through arms-control agreements.

Iran's intransigence is both deeply unfortunate and perfectly predictable. It is unfortunate because Tehran's refusal to suspend its uranium-enrichment operations immediately--as demanded in July by the U.N. Security Council in a legally binding resolution--suggests that Iran is moving more quickly than expected toward a nuclear-weapons capability. Tehran has now turned the nuclear crisis into a test of the whole U.N. Security Council system. And Russia and China's current position, threatening to veto any biting sanctions against Iran, suggests that the Security Council may well fail this crucial test.

Tehran's response is predictable, however, because the offer on the table contains both inadequate economic carrots and barely credible threats of sanctions and military force. The carrots appeared impressive at first glance--in return for a suspension of enrichment we reportedly promised to provide light-water nuclear reactors and to help Iran with civil aviation and telecommunications technology. But we did not offer the one incentive that might possibly work, security guarantees that could reduce Iran's desire for nuclear weapons.

This omission is striking. The Iranian government can't talk openly about their security concerns because that would blow their cover story that the nuclear program is only for energy production. And Washington does not want to discuss such worries because it wants to keep open the possibility of removing the regime by force. "Security assurances are not on the table," U.S. Secretary of State Condoleezza Rice too cleverly argued this spring: "It is a little strange to talk about security guarantees ... I thought the Iranian position was that they weren't developing a nuclear bomb."

This is partly a crisis of our own making, as the Bush administration has practiced the reverse of Teddy Roosevelt's maxim--speaking loudly and carrying a small stick. Think about how Tehran reacted when Bush stated (in his second Inaugural Address), "The rulers of outlaw regimes can know that we still believe as Abraham Lincoln did: 'Those who deny freedoms to others deserve it not for themselves; and, under the rule of a just God, cannot long retain it." Or when Bush dramatically told reporters last April that "all options are on the table," in direct response to a question about whether he was considering a nuclear attack against Iran. Such statements only encourage Iran to develop a nuclear deterrent quickly, before the United States can carry out its perceived aggressive intent. Last month, Iran's National Security Council Secretary Ali Larijani pointedly complained about such rhetoric. "How can a side that wants to topple the regime also attempt to negotiate?"

Given the current vulnerability of U.S. forces in Iraq, the deteriorating situation in Afghanistan, and the lack of Israeli success against Hizbullah, Iranian officials seem confident that they face no immediate threat of a U.S. military assault. But they are clearly worried that Bush just might attack Iran right before he leaves office in January 2009, or that his successor might do so once U.S. forces withdraw from Iraq.

The best way to prevent a nuclear Iran is for Washington to offer the kind of security assurances that might reduce support in Tehran for building a nuclear arsenal. It will be hard to make such assurances credible, but a public U.S. promise to take forcible regime change off the table, and a U.N. Security Council commitment to protect the "political sovereignty" of Iran could help. Involving the Security Council could also pull China and Russia back into the nonproliferation coalition and enhance the U.N.'s legitimacy.

There is very little time left, which means negotiations should begin despite Iran's unfortunate opening position. Tehran's response reportedly indicated a willingness to negotiate all aspects of its nuclear program, so working out an agreement for Iran to limit itself to low-level uranium enrichment might still be possible. This would work only if Tehran accepts full IAEA inspections and a freeze on future centrifuge construction. Will they? The one thing that might cause Tehran to do so, and that would compensate for any loss of face, would be an assurance that the United States will not launch another preventive war, as it did in Iraq, to remove the Iranian regime. If in turn we get a nuclear-free Iran, that's a good deal for the West as well.