Considering that Iran is listed by the U.S. State Department as the world's No. 1 state sponsor of terrorism (and Americans are one of its main victims), that is disquieting news. The dangers were well summed up by another bipartisan report, this one issued by former Senators Chuck Robb and Dan Coats: "Iran's nuclear development may pose the most significant strategic threat to the United States during the next Administration. A nuclear-ready or nuclear-armed Islamic Republic ruled by the clerical regime could threaten the Persian Gulf region and its vast energy resources, spark nuclear proliferation throughout the Middle East, inject additional volatility into global energy markets, embolden extremists in the region and destabilize states such as Saudi Arabia and others in the region, provide nuclear technology to other radical regimes and terrorists (although Iran might hesitate to share traceable nuclear technology), and seek to make good on its threats to eradicate Israel."

No wonder there is general agreement across the U.S. political spectrum that, as President-elect Barack Obama said in the second presidential debate in October, "We cannot allow Iran to get a nuclear weapon." Yet what is he actually prepared to do to stop the mullahs?

Bush relied on tough talk and toothless diplomacy conducted by France, Britain, and Germany. Those negotiations went nowhere, but that doesn't discourage Obama from vowing to place even more emphasis on diplomacy once he takes office. He has vowed to use "sticks" as well as "carrots" but, given the opposition of China and Russia in particular, there is scant cause to think that he will be any more successful than Bush in putting real multilateral pressure on Iran. Indeed, an Iranian spokesman has already rejected Obama's approach, saying, "Tehran's stand is the same as before; that is, if they [the U.S. administration] want suspension, we have repeatedly announced that we will not suspend [enrichment activities]."

The likelihood is that the Iranians will continue to string Obama along, as they've strung along the Europeans, drawing out the negotiations to give themselves time to produce a bomb. Once they actually go nuclear, they realize from observing North Korea's experience that their leverage to demand concessions from the West will soar and the West's capacity for an effective response will plummet. (North Korea is another country where Bush has done little to head off a serious threat.)

For all the empty talk of "tough diplomacy," the uncomfortable reality is that there is only one option that in the short term is likely to forestall Iran from going nuclear: airstrikes on its atomic installations. That is hardly an ideal solution, and, given how dispersed and protected Iran's nuclear facilities are, not even a series of sorties is likely to eradicate the threat. But bombing could at least set back the Iranian program for a number of years, which is more than diplomacy is likely to accomplish.

Bush has implicitly threatened such a strike when he has said time after time that "all options are on the table," but he has never made any moves to prepare either the U.S. military or the U.S. public for such action. Some reports suggest he went so far as to discourage Israel from mounting its own raid.

No doubt President-elect Obama is listening to the numerous voices inside and outside his incoming administration that cite the many drawbacks of an attack on Iran. And, no question, the drawbacks are real. These range from the possibility of the Iranian people rallying around the mullahs to the possibility of the mullahs closing the Strait of Hormuz or carrying out terrorist strikes on U.S. forces in Iraq, Afghanistan, or as far afield as Europe or the Americas.

There are even greater potential pitfalls associated with a serious attempt to stamp out terrorism emanating from Pakistan. "Preemption lite" -- the current approach of picking off terrorist leaders with armed Predator drones -- can help to weaken and slow the jihadists, but it can hardly defeat them. That would, in all likelihood, require an invasion of western Pakistan, perhaps accompanied by preemptive airstrikes on Pakistan's nuclear installations. That is an undertaking so daunting as to make even the most hawkish of analysts turn dovish.

Pakistan is, after all, a country of 160 million people with nuclear weapons and more than 600,000 active-duty military personnel. Even if most of its armed forces could be convinced not to resist a large-scale, U.S.-led incursion (and that is by no means a certainty), the invading troops would have to deal with the nightmarish prospect of pacifying the Federally Administered Tribal Areas. This region is home to more than 6 million Pashtuns living amid treacherous, mountainous terrain that has never been fully brought under control by any outside power. Next door is the North-West Frontier Province, which has a population of 20 million and has also become a playground for jihadists. Sending U.S. troops to take on such a difficult task would be virtually unthinkable, barring another tragedy on the scale of 9/11.

And that's precisely the point. We Americans shy away from preemptive action because we can imagine all too clearly the costs of action. But we lack the imagination to see the costs of inaction. Or, rather, we can imagine the costs, but we tell ourselves, fingers crossed, that we may never have to pay them. Perhaps we will not live to see a major attack, emanating from Pakistan or Iran, on our soil or the soil of an allied country. Perhaps we will indeed dodge the bullet -- or, more aptly, the bomb. Or perhaps not.

In a prosperous democracy it is all too easy for our leaders to succumb to the same soothing narcosis as the general populace, content to imagine that problems do not really exist because they have not yet fully materialized. That is the illusion that Churchill fought against in the 1930s and Clarke in the 1990s. They both failed. Now, as the United States and our allies fail to act decisively against present-day dangers, we know why.