Faced with the spectacle of Mahmoud Ahmadinejad crowing over the humiliation of Britain and exulting over the prospect of Iran becoming a nuclear power, it is hard not to succumb to despair. W.B. Yeats had words for our present predicament: “The best lack all conviction, while the worst / Are full of passionate intensity.”

There is no point in denying the terrible harm that the hostage affair has done to the British armed forces. It is not just the lack of moral or physical courage displayed by the 15 hostages, who seem not to have been properly trained to deal with captivity. Even more damaging has been the revelation that the unprofessional conduct of the sailors and marines is regarded by their commanders as heroic.

Worst of all has been the sheer incompetence with which the politicians have handled the whole sorry business, from tying the navy’s hands and appeasing rather than defying Tehran to allowing the hostages to sell their stories to the press. One of the West’s most valuable assets has been seriously compromised. It is scarcely an exaggeration to say that this hostage affair has damaged the reputation of Britain’s armed forces as grievously as Abu Ghraib did America’s.

Meanwhile, Iran’s nuclear program goes full steam ahead. Mr. Ahmadinejad is evidently at pains to persuade us that it has passed the point of no return. Whether or not the experts believe him is beside the point. Iran now appears to have enough political momentum to ignore sanctions, protests, and all the other weapons in the diplomatic arsenal.

The fact that Russia and China refused to support the British when their personnel were seized on a U.N. mission, while Europe offered only token support, speaks volumes. These powers are already reconciled to a nuclear Iran and in some cases are even gloating over the prospect.

This is why the military option is so important. It was always a last resort — but last resorts sometimes have to be resorted to.

Ultimately, it all comes down to President Bush. He alone has the power to stop Iran’s nuclear program in its tracks, before it is too late. Most of Iran’s neighbors have been privately begging him to do precisely what America’s allies — with the exception of Israel — have been warning against. Mr. Bush knows that even if destroying Iran’s nuclear facilities is morally the right thing to do, he will be condemned even by those who stand to gain most — again with the exception of Israel.

The loneliness of a leader in such a unique predicament is literally inconceivable. A friend who has spent time with the president both in December and last month tells me that there has been a distinct change in his demeanor. He says that Mr. Bush seems much more somber and feels much more isolated than he did even a few months ago. This is partly the accumulated cares of office; partly that he has had to part with trusted colleagues, and partly also that he has had to endure hurtful criticism even from Republican candidates eager to replace him.

But Mr. Bush’s mood is also a symptom of something deeper: the existential isolation that comes with the hardest job in the world. To the burden of being president is added that of being commander in chief at a time when the West faces its most dangerous challenge for a generation. No one can share that burden.

No one, that is, except God. There are those who ridicule this president for his open reliance on prayer and his rare but transparently sincere invocations of the Almighty. Where else, though, could George Bush turn — confronted as he is with the necessity of removing a deadly threat to the survival, not only of Israel, but of the free world? The acute consciousness that his decisions are subject to not only human but also divine judgment imposes moral checks and balances on the president that are lacking in narrowly secular minds.

As the West approaches the moment of truth in its efforts to resist Iranian aggression, I for one am glad that the president of America is not a Machiavellian “realist” who acknowledges no moral law above self-interest. What Yeats called the “passionate intensity” of the enemies of civilization is a quality that Mr. Ahmadinejad has in abundance. All too often in history, such intensity has proved more than a match for the apostles of Realpolitik.

Those hostile to religion in general, who often do not differentiate between religions, should ask themselves whether Mr. Bush’s faith does not differ from Mr. Ahmadinejad’s in one crucial respect: the former wishes to prevent the end of the world, while the latter wishes to bring it about. This clash between civilization and barbarism is not about the rival claims of different gods. It is rather a conflict between those for whom faith is the ultimate guarantee of freedom and those for whom faith is a warrant for fanaticism.